fix error while compiling against 4.4.194 kernel version

[ahtabrizi]

While building the repo against Linux kernel version 4.4.194 (on arm device) it throws the following error:

Building v4l2-loopback driver...
make -C /lib/modules/`uname -r`/build M=/home/firefly/v4l2loopback KCPPFLAGS="-DSNAPSHOT_VERSION='"0.12.7-387-g2c9b670"'" modules
make[1]: Entering directory '/usr/src/linux-headers-4.4.194'
  CC [M]  /home/firefly/v4l2loopback/v4l2loopback.o
In file included from include/linux/printk.h:6:0,
                 from include/linux/kernel.h:13,
                 from include/linux/list.h:8,
                 from include/linux/preempt.h:10,
                 from include/linux/spinlock.h:50,
                 from include/linux/vmalloc.h:4,
                 from /home/firefly/v4l2loopback/v4l2loopback.c:17:
/home/firefly/v4l2loopback/v4l2loopback.c: In function 'vidioc_qbuf':
include/linux/kern_levels.h:4:18: warning: format '%lld' expects argument of type 'long long int', but argument 11 has type '__kernel_time_t {aka long int}' [-Wformat=]
error, forbidden warning:kern_levels.h:4
 #define KERN_SOH "\001"  /* ASCII Start Of Header */
                  ^
include/linux/kern_levels.h:13:19: note: in expansion of macro 'KERN_SOH'
 #define KERN_INFO KERN_SOH "6" /* informational */
                   ^~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:89:11: note: in expansion of macro 'KERN_INFO'
    printk(KERN_INFO "v4l2-loopback[" __stringify( \
           ^~~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:1698:3: note: in expansion of macro 'dprintkrw'
   dprintkrw(
   ^~~~~~~~~
include/linux/kern_levels.h:4:18: warning: format '%lld' expects argument of type 'long long int', but argument 11 has type '__kernel_time_t {aka long int}' [-Wformat=]
error, forbidden warning:kern_levels.h:4
 #define KERN_SOH "\001"  /* ASCII Start Of Header */
                  ^
include/linux/kern_levels.h:13:19: note: in expansion of macro 'KERN_SOH'
 #define KERN_INFO KERN_SOH "6" /* informational */
                   ^~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:89:11: note: in expansion of macro 'KERN_INFO'
    printk(KERN_INFO "v4l2-loopback[" __stringify( \
           ^~~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:1707:3: note: in expansion of macro 'dprintkrw'
   dprintkrw(
   ^~~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c: In function 'vidioc_dqbuf':
include/linux/kern_levels.h:4:18: warning: format '%lld' expects argument of type 'long long int', but argument 11 has type '__kernel_time_t {aka long int}' [-Wformat=]
error, forbidden warning:kern_levels.h:4
 #define KERN_SOH "\001"  /* ASCII Start Of Header */
                  ^
include/linux/kern_levels.h:13:19: note: in expansion of macro 'KERN_SOH'
 #define KERN_INFO KERN_SOH "6" /* informational */
                   ^~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:89:11: note: in expansion of macro 'KERN_INFO'
    printk(KERN_INFO "v4l2-loopback[" __stringify( \
           ^~~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:1828:3: note: in expansion of macro 'dprintkrw'
   dprintkrw(
   ^~~~~~~~~
include/linux/kern_levels.h:4:18: warning: format '%lld' expects argument of type 'long long int', but argument 11 has type '__kernel_time_t {aka long int}' [-Wformat=]
error, forbidden warning:kern_levels.h:4
 #define KERN_SOH "\001"  /* ASCII Start Of Header */
                  ^
include/linux/kern_levels.h:13:19: note: in expansion of macro 'KERN_SOH'
 #define KERN_INFO KERN_SOH "6" /* informational */
                   ^~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:89:11: note: in expansion of macro 'KERN_INFO'
    printk(KERN_INFO "v4l2-loopback[" __stringify( \
           ^~~~~~~~~
/home/firefly/v4l2loopback/v4l2loopback.c:1847:3: note: in expansion of macro 'dprintkrw'
   dprintkrw(
   ^~~~~~~~~
scripts/Makefile.build:283: recipe for target '/home/firefly/v4l2loopback/v4l2loopback.o' failed
make[2]: *** [/home/firefly/v4l2loopback/v4l2loopback.o] Error 1
Makefile:1479: recipe for target '_module_/home/firefly/v4l2loopback' failed
make[1]: *** [_module_/home/firefly/v4l2loopback] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-4.4.194'
Makefile:51: recipe for target 'v4l2loopback.ko' failed
make: *** [v4l2loopback.ko] Error 2

This PR fixes this issue.

[umlaeute]

this in turn breaks building on 64bit platforms (so I'm closing this).

a proper way would be to just cast the buf->timestamp.tv_sec to long long int. and leave the format-specifier as is.

feel free to open a new PR (based on current main)