ATM: mpc, fix use after free

Stanse found that mpc_push frees skb and then it dereferences it. It
is a typo, new_skb should be dereferenced there.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/mpc.c

@@ -778,7 +778,7 @@ static void mpc_push(struct atm_vcc *vcc, struct sk_buff *skb)
 	eg->packets_rcvd++;
 	mpc->eg_ops->put(eg);
 
-	memset(ATM_SKB(skb), 0, sizeof(struct atm_skb_data));
+	memset(ATM_SKB(new_skb), 0, sizeof(struct atm_skb_data));
 	netif_rx(new_skb);
 }