Fix possible warnings on macOS

[triplef]

Fixes the following warnings (or in our case errors when building with -Werror):

hid.c:420:45: error: variable 'entry_id' may be uninitialized when used here [-Werror,-Wconditional-uninitialized]
                        sprintf(cur_dev->path, "DevSrvsID:%llu", entry_id);
                                                                 ^~~~~~~~
In module 'Darwin' imported from hid.c:30:
/Applications/Xcode-13.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/secure/_stdio.h:47:56: note: expanded from macro 'sprintf'
  __builtin___sprintf_chk (str, 0, __darwin_obsz(str), __VA_ARGS__)
                                                       ^~~~~~~~~~~
hid.c:384:19: note: initialize the variable 'entry_id' to silence this warning
        uint64_t entry_id;
                         ^
                          = 0
hid.c:908:10: error: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
                return length;
                ~~~~~~ ^~~~~~
hid.c:942:10: error: implicit conversion loses integer precision: 'CFIndex' (aka 'long') to 'int' [-Werror,-Wshorten-64-to-32]
                return report_length;
                ~~~~~~ ^~~~~~~~~~~~~
hid.c:964:9: error: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'int' [-Werror,-Wshorten-64-to-32]
        return len;
        ~~~~~~ ^~~