tcp: Remove unused but set variable

Remove the unused but set variable icsk in listening_get_next to fix the
following GCC warning when building with 'W=1':

  net/ipv4/tcp_ipv4.c: In function ‘listening_get_next’:
  net/ipv4/tcp_ipv4.c:1890:31: warning: variable ‘icsk’ set but not used [-Wunused-but-set-variable]
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_ipv4.c

@@ -1887,7 +1887,6 @@ static void *listening_get_next(struct seq_file *seq, void *cur)
 	struct tcp_iter_state *st = seq->private;
 	struct net *net = seq_file_net(seq);
 	struct inet_listen_hashbucket *ilb;
-	struct inet_connection_sock *icsk;
 	struct sock *sk = cur;
 
 	if (!sk) {
@@ -1909,7 +1908,6 @@ static void *listening_get_next(struct seq_file *seq, void *cur)
 			continue;
 		if (sk->sk_family == st->family)
 			return sk;
-		icsk = inet_csk(sk);
 	}
 	spin_unlock_bh(&ilb->lock);
 	st->offset = 0;