pkt_sched: Fix "parent is root" test in qdisc_create().

As noticed by Stephen Hemminger, the root qdisc is denoted by
TC_H_ROOT, not zero.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -792,7 +792,7 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
 				goto err_out3;
 			}
 		}
-		if (parent && !(sch->flags & TCQ_F_INGRESS))
+		if ((parent != TC_H_ROOT) && !(sch->flags & TCQ_F_INGRESS))
 			list_add_tail(&sch->list, &dev_queue->qdisc->list);
 
 		return sch;