pkt_sched: remove unnecessary xchg() in packet schedulers

The use of xchg() hasn't been necessary since 2.2.something when proper
locking was added to packet schedulers.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 83f5e69..3a119f5 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1100,7 +1100,9 @@
 		    == NULL)
 			return -ENOBUFS;
 		sch_tree_lock(sch);
-		if ((*old = xchg(&cl->un.leaf.q, new)) != NULL) {
+		*old = cl->un.leaf.q;
+		cl->un.leaf.q = new;
+		if (*old != NULL) {
 			qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
 			qdisc_reset(*old);
 		}