drivers: socketcan: fix assigned but unused variable
drivers: socketcan: fix assigned but unused variable

The id variable was meant to be used in the TX callback, since there's a
possible race from the MBOX_FREE to txcb is called.

Signed-off-by: Jeppe Ledet-Pedersen <04ca46c996f3ce83ad557eea1980ca8ca065ba1b@satlab.org>

libcsp/libcsp,Psykar/kubos,marshall/libcsp,libcsp/libcsp,GomSpace/libcsp,Psykar/kubos,kubostech/KubOS,GomSpace/libcsp,pacheco017/libcsp,Psykar/kubos,satlab/libcsp,marshall/libcsp,pacheco017/libcsp,marshall/libcsp,Psykar/kubos,Psykar/kubos,pacheco017/libcsp,satlab/libcsp,Psykar/kubos,pacheco017/libcsp,GomSpace/libcsp,kubostech/KubOS,satlab/libcsp,Psykar/kubos