cgroup: re-use the parent pointer in cgroup_destroy_locked()

As we already have a pointer to the parent cgroup in
cgroup_destroy_locked(), we don't need to calculate it again
to pass as an argument for cgroup1_check_for_release().

Signed-off-by: Roman Gushchin <guro@fb.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kernel-team@fb.com
Cc: linux-kernel@vger.kernel.org

kernel/cgroup/cgroup.c

@@ -5022,7 +5022,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 		tcgrp->nr_dying_descendants++;
 	}
 
-	cgroup1_check_for_release(cgroup_parent(cgrp));
+	cgroup1_check_for_release(parent);
 
 	/* put the base reference */
 	percpu_ref_kill(&cgrp->self.refcnt);