gfs2: Remove unnecessary function prototype

Function __gfs2_glock_dq() gets defined before it is used, so there is
no need for a separate function declaration.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -61,7 +61,6 @@ struct gfs2_glock_iter {
 typedef void (*glock_examiner) (struct gfs2_glock * gl);
 
 static void do_xmote(struct gfs2_glock *gl, struct gfs2_holder *gh, unsigned int target);
-static void __gfs2_glock_dq(struct gfs2_holder *gh);
 static void handle_callback(struct gfs2_glock *gl, unsigned int state,
 			    unsigned long delay, bool remote);