Suppress unused variable warning in mfi.c
With clang 15, the following -Werror warnings are produced:
sys/dev/mfi/mfi.c:3698:6: error: variable 'timedout' set but not used [-Werror,-Wunused-but-set-variable]
int timedout;
^
sys/dev/mfi/mfi.c:3742:6: error: variable 'timedout' set but not used [-Werror,-Wunused-but-set-variable]
int timedout = 0;
^
Here, 'timedout' are variables that are only used when debugging,
requiring #if 0 statements to be modified. Mark the variables as
potentially unused, to suppress the warnings.
MFC after: 3 days
(cherry picked from commit
3dbe05f61b65a73582aefdc2ee5a50ad2b4390ef)