can: peak_usb: pcan_usb_get_serial(): remove error message from error path

The caller of pcan_usb_get_serial() already prints an error message,
so remove this one and return immediately.

Link: https://lore.kernel.org/r/20210406111622.1874957-8-mkl@pengutronix.deAcked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Tested-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/peak_usb/pcan_usb.c

@@ -365,16 +365,17 @@ static int pcan_usb_get_serial(struct peak_usb_device *dev, u32 *serial_number)
 	int err;
 
 	err = pcan_usb_wait_rsp(dev, PCAN_USB_CMD_SN, PCAN_USB_GET, args);
-	if (err) {
-		netdev_err(dev->netdev, "getting serial failure: %d\n", err);
-	} else if (serial_number) {
+	if (err)
+		return err;
+
+	if (serial_number) {
 		__le32 tmp32;
 
 		memcpy(&tmp32, args, 4);
 		*serial_number = le32_to_cpu(tmp32);
 	}
 
-	return err;
+	return 0;
 }
 
 /*