net/sched: fq_codel: Avoid set-but-unused variable

The code introduced by commit 2ccccf5f ("net_sched: update
hierarchical backlog too") only sets prev_backlog in fq_codel_dequeue()
but not using that anywhere, remove that setting.

Cc: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_fq_codel.c

@@ -288,7 +288,6 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
 	struct fq_codel_flow *flow;
 	struct list_head *head;
 	u32 prev_drop_count, prev_ecn_mark;
-	unsigned int prev_backlog;
 
 begin:
 	head = &q->new_flows;
@@ -307,7 +306,6 @@ static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
 
 	prev_drop_count = q->cstats.drop_count;
 	prev_ecn_mark = q->cstats.ecn_mark;
-	prev_backlog = sch->qstats.backlog;
 
 	skb = codel_dequeue(sch, &sch->qstats.backlog, &q->cparams,
 			    &flow->cvars, &q->cstats, qdisc_pkt_len,