gfs2: remove dead code in add_to_queue

clang static analyzer complains that value stored to 'gh' is never read.
The code of this line is useless after commit 0b93bac2
("gfs2: Remove LM_FLAG_PRIORITY flag"). Remove this code to save space.
Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

fs/gfs2/glock.c

@@ -1524,7 +1524,6 @@ __acquires(&gl->gl_lockref.lock)
 		return;
 	}
 	list_add_tail(&gh->gh_list, insert_pt);
-	gh = list_first_entry(&gl->gl_holders, struct gfs2_holder, gh_list);
 	spin_unlock(&gl->gl_lockref.lock);
 	if (sdp->sd_lockstruct.ls_ops->lm_cancel)
 		sdp->sd_lockstruct.ls_ops->lm_cancel(gl);