tun: Remove a dead line of code

Remove an unnecessary assignment.
Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -995,7 +995,6 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 				goto err_free_sk;
 		}
 
-		err = -EINVAL;
 		err = register_netdevice(tun->dev);
 		if (err < 0)
 			goto err_free_sk;