act_mirred: fix a typo in get_dev

Fixes: 255cb30425c0 ("net/sched: act_mirred: Add new tc_action_ops get_dev()")
Cc: Hadar Hen Zion <hadarh@mellanox.com>
Cc: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_mirred.c

@@ -321,7 +321,7 @@ static int tcf_mirred_device(const struct tc_action *a, struct net *net,
 	int ifindex = tcf_mirred_ifindex(a);
 
 	*mirred_dev = __dev_get_by_index(net, ifindex);
-	if (!mirred_dev)
+	if (!*mirred_dev)
 		return -EINVAL;
 	return 0;
 }