pkt_sched: Fix dev_graft_qdisc() locking

During dev_graft_qdisc() dev is deactivated, so qdisc_root_lock()
returns wrong lock of noop_qdisc instead of qdisc_sleeping.
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -624,7 +624,7 @@ static struct Qdisc *dev_graft_qdisc(struct netdev_queue *dev_queue,
 	struct Qdisc *oqdisc = dev_queue->qdisc_sleeping;
 	spinlock_t *root_lock;
 
-	root_lock = qdisc_root_lock(oqdisc);
+	root_lock = qdisc_lock(oqdisc);
 	spin_lock_bh(root_lock);
 
 	/* Prune old scheduler */