can: xilinx: fix return type of ndo_start_xmit function

The method ndo_start_xmit() is defined as returning an 'netdev_tx_t',
which is a typedef for an enum type, so make sure the implementation in
this driver has returns 'netdev_tx_t' value, and change the function
return type to netdev_tx_t.

Found by coccinelle.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/xilinx_can.c

@@ -612,7 +612,7 @@ static int xcan_start_xmit_mailbox(struct sk_buff *skb, struct net_device *ndev)
  *
  * Return: NETDEV_TX_OK on success and NETDEV_TX_BUSY when the tx queue is full
  */
-static int xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
+static netdev_tx_t xcan_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
 	struct xcan_priv *priv = netdev_priv(ndev);
 	int ret;