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

Freeing netdev without free_netdev() leads to net, tx leaks.
And it may lead to dereferencing freed pointer.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/lantiq_etop.c b/drivers/net/ethernet/lantiq_etop.c
index 6a21274..bfdb0686 100644
--- a/drivers/net/ethernet/lantiq_etop.c
+++ b/drivers/net/ethernet/lantiq_etop.c
@@ -769,7 +769,7 @@
 	return 0;
 
 err_free:
-	kfree(dev);
+	free_netdev(dev);
 err_out:
 	return err;
 }