[NET_SCHED]: Revert "HTB: fix incorrect use of RB_EMPTY_NODE"

With commit 10fd48f2376db52f08bf0420d2c4f580e39269e1 [1] ,  RB_EMPTY_NODE
changed behaviour so it returns true when the node is empty as expected.
Hence Patrick McHardy's fix for sched_htb.c should be reverted.

Signed-off-by: Ismail Donmez <ismail@pardus.org.tr>
ACKed-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -391,7 +391,7 @@ static inline void htb_add_class_to_row(struct htb_sched *q,
 /* If this triggers, it is a bug in this code, but it need not be fatal */
 static void htb_safe_rb_erase(struct rb_node *rb, struct rb_root *root)
 {
-	if (!RB_EMPTY_NODE(rb)) {
+	if (RB_EMPTY_NODE(rb)) {
 		WARN_ON(1);
 	} else {
 		rb_erase(rb, root);