Adjust pcmlog_{initialize,shutdown}() definitions to avoid clang 15 warning

Adjust pcmlog_{initialize,shutdown}() definitions to avoid clang 15 warning

With clang 15, the following -Werror warnings are produced:

    sys/dev/hwpmc/hwpmc_logging.c:1228:18: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
    pmclog_initialize()
                     ^
                      void
    sys/dev/hwpmc/hwpmc_logging.c:1277:16: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
    pmclog_shutdown()
                   ^
                    void

This is because pcmlog_{initialize,shutdown}() 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 ba95c556029357800d18a5bc5abd02a2b7d0c9de)