staging: lustre: mgc: make llog_process_lock static

Fix following sparse warning.
mgc_request.c:376:1:
warning: symbol 'llog_process_lock' was not declared. Should it be static?

Signed-off-by: Sandeep Jain <sandeepjain.linux@gmail.com>
Acked-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>