net: allwinner: Fix use correct return type for ndo_start_xmit()

The method ndo_start_xmit() returns a value of type netdev_tx_t. Fix
the ndo function to use the correct type. And emac_start_xmit() can
leak one skb if 'channel' == 3.
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/allwinner/sun4i-emac.c

@@ -417,7 +417,7 @@ static void emac_timeout(struct net_device *dev, unsigned int txqueue)
 /* Hardware start transmission.
  * Send a packet to media from the upper layer.
  */
-static int emac_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t emac_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct emac_board_info *db = netdev_priv(dev);
 	unsigned long channel;
@@ -425,7 +425,7 @@ static int emac_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	channel = db->tx_fifo_stat & 3;
 	if (channel == 3)
-		return 1;
+		return NETDEV_TX_BUSY;
 
 	channel = (channel == 1 ? 1 : 0);