cgroup: fix obsolete function name in cgroup_destroy_locked()

Since commit e76ecaee ("cgroup: use cgroup_kn_lock_live() in other
cgroup kernfs methods"), cgroup_kn_lock_live() is used in cgroup kernfs
methods. Update corresponding comment.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -5871,7 +5871,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 	/*
 	 * Mark @cgrp and the associated csets dead.  The former prevents
 	 * further task migration and child creation by disabling
-	 * cgroup_lock_live_group().  The latter makes the csets ignored by
+	 * cgroup_kn_lock_live().  The latter makes the csets ignored by
 	 * the migration path.
 	 */
 	cgrp->self.flags &= ~CSS_ONLINE;