rionet: use free_netdev(netdev) instead of kfree()

Freeing netdev without free_netdev() leads to net, tx leaks.
I might lead to dereferencing freed pointer.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

@@
struct net_device* dev;
@@

-kfree(dev)
+free_netdev(dev)
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/rionet.c

@@ -384,7 +384,7 @@ static void rionet_remove(struct rio_dev *rdev)
 	free_pages((unsigned long)rionet_active, rdev->net->hport->sys_size ?
 					__ilog2(sizeof(void *)) + 4 : 0);
 	unregister_netdev(ndev);
-	kfree(ndev);
+	free_netdev(ndev);
 
 	list_for_each_entry_safe(peer, tmp, &rionet_peers, node) {
 		list_del(&peer->node);