Adjust function definition in subr_devmap.c to avoid clang 15 warning

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

sys/kern/subr_devmap.c:87:19: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
devmap_print_table()
                  ^
                   void

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

Sponsored by: The FreeBSD Foundation

(cherry picked from commit 8e9ca1379edad98a957570a2339a9236910e61c1)