Adjust function definitions in geom_event.c to avoid clang 15 warnings
With clang 15, the following -Werror warnings are produced:
sys/geom/geom_event.c:261:13: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] g_run_events() ^ void sys/geom/geom_event.c:405:12: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] g_do_wither() ^ void sys/geom/geom_event.c:449:13: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes] g_event_init() ^ void
This is because g_run_events(), g_do_wither(), and g_event_init() are
declared with (void) argument lists, but defined with empty argument
lists. Make the definitions match the declarations.
MFC after: 3 days
(cherry picked from commit ac3153434fcc3ddcbb47c7f397a1bc34fd0e0dcb)