Adjust function definition in arm's mv_common.c to avoid clang 15 warning

With clang 15, the following -Werror warning is produced:

sys/arm/mv/mv_common.c:414:20: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
mv_check_soc_family()
                   ^
                    void

This is because mv_check_soc_family() is declared with a (void) argument
list, but defined with an empty argument list. Make the definition match
the declaration.

MFC after: 3 days