can: rcar_can: print request_irq() error code

Also print the error code when the request_irq() call fails in rcar_can_open(),
rewording  the error message...
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rcar_can.c

@@ -527,7 +527,8 @@ static int rcar_can_open(struct net_device *ndev)
 	napi_enable(&priv->napi);
 	err = request_irq(ndev->irq, rcar_can_interrupt, 0, ndev->name, ndev);
 	if (err) {
-		netdev_err(ndev, "error requesting interrupt %d\n", ndev->irq);
+		netdev_err(ndev, "request_irq(%d) failed, error %d\n",
+			   ndev->irq, err);
 		goto out_close;
 	}
 	can_led_event(ndev, CAN_LED_EVENT_OPEN);