sch_sfq: fix null pointer dereference on init failure

Currently only a memory allocation failure can lead to this, so let's
initialize the timer first.

Fixes: 6529eab ("net: sched: introduce tcf block infractructure")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_sfq.c

@@ -716,13 +716,13 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
 	int i;
 	int err;
 
+	setup_deferrable_timer(&q->perturb_timer, sfq_perturbation,
+			       (unsigned long)sch);
+
 	err = tcf_block_get(&q->block, &q->filter_list);
 	if (err)
 		return err;
 
-	setup_deferrable_timer(&q->perturb_timer, sfq_perturbation,
-			       (unsigned long)sch);
-
 	for (i = 0; i < SFQ_MAX_DEPTH + 1; i++) {
 		q->dep[i].next = i + SFQ_MAX_FLOWS;
 		q->dep[i].prev = i + SFQ_MAX_FLOWS;