atm: Do not free already unregistered net device.

Both br2684_push and br2684_exit do so, but unregister_netdev()
releases the device itself.

Signed-off-by: Pavel Emelyanov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/atm/br2684.c

···
 			list_del(&brdev->br2684_devs);
 			read_unlock(&devs_lock);
 			unregister_netdev(net_dev);
-			free_netdev(net_dev);
 		}
 		return;
 	}
···
 
 		list_del(&brdev->br2684_devs);
 		unregister_netdev(net_dev);
-		free_netdev(net_dev);
 	}
 }