[GFS2] sem -> mutex conversion in locking.c

Convert a semaphore to a mutex in locking.c and also tidy
up one or two loose ends.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/util.h

@@ -30,7 +30,6 @@ void gfs2_assert_i(struct gfs2_sbd *sdp);
 do { \
 	if (unlikely(!(assertion))) { \
 		gfs2_assert_i(sdp); \
-		BUG(); \
         } \
 } while (0)