caif: fix caif_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.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/caif/caif_serial.c

@@ -266,7 +266,7 @@ static int handle_tx(struct ser_device *ser)
 	return tty_wr;
 }
 
-static int caif_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t caif_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ser_device *ser;