caif: fix cfspi_xmit()'s return type

The method ndo_start_xmit() is defined as returning an 'netdev_tx_t',
which is a typedef for an enum type, but the implementation in this
driver returns an 'int'.

Fix this by returning 'netdev_tx_t' in this driver too and
returning NETDEV_TX_OK instead of 0 accordingly.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/caif/caif_spi.c

@@ -488,7 +488,7 @@ static void cfspi_xfer_done_cb(struct cfspi_ifc *ifc)
 	complete(&cfspi->comp);
 }
 
-static int cfspi_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t cfspi_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct cfspi *cfspi = NULL;
 	unsigned long flags;
@@ -514,7 +514,7 @@ static int cfspi_xmit(struct sk_buff *skb, struct net_device *dev)
 		cfspi->cfdev.flowctrl(cfspi->ndev, 0);
 	}
 
-	return 0;
+	return NETDEV_TX_OK;
 }
 
 int cfspi_rxfrm(struct cfspi *cfspi, u8 *buf, size_t len)