net/can: fix the typo and compile error

[zhhyu7]

Summary

Otherwise, we can only manually enable NET_WRITE_BUFFERS

Impact

net/can/can_sendmsg_buffered.c

Testing

Since no code logic was modified, only the compilation was verified.
sim:matter with enable CONFIG_NET_CAN and CONFIG_NET_CAN_WRITE_BUFFERS
.config

nuttx$ cat .config | grep NET_CAN
CONFIG_NET_CANPROTO_OPTIONS=y
CONFIG_NET_CAN=y
CONFIG_NET_CAN_WRITE_BUFFERS=y
# CONFIG_NET_CAN_EXTID is not set
CONFIG_NET_CAN_SOCK_OPTS=y
CONFIG_NET_CAN_RAW_FILTER_MAX=32
# CONFIG_NET_CAN_NOTIFIER is not set

build log

nuttx$ make -j12
Create version.h
LD:  nuttx
Pac SIM with dynamic libs..
'/lib/x86_64-linux-gnu/libz.so.1' -> 'sim-pac/libs/libz.so.1'
'/lib/x86_64-linux-gnu/libc.so.6' -> 'sim-pac/libs/libc.so.6'
'/lib64/ld-linux-x86-64.so.2' -> 'sim-pac/ld-linux-x86-64.so.2'
SIM elf with dynamic libs archive in nuttx.tgz
nuttx$ ls -l nuttx
-rwxrwxr-x 1 zhhyu zhhyu 4544616 12月 24 20:54 nuttx