can: peak_usb: pcan_usb_get_serial(): unconditionally assign serial_number

The function serial_number is only called from one location with a
valid serial_number pointer. Remove not needed NULL pointer check.

Link: https://lore.kernel.org/r/20210406111622.1874957-10-mkl@pengutronix.deAcked-by: NStephane Grosjean <s.grosjean@peak-system.com>
Tested-by: NStephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

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

@@ -367,9 +367,7 @@ static int pcan_usb_get_serial(struct peak_usb_device *dev, u32 *serial_number)
 	err = pcan_usb_wait_rsp(dev, PCAN_USB_CMD_SN, PCAN_USB_GET, args);
 	if (err)
 		return err;
-
-	if (serial_number)
-		*serial_number = le32_to_cpup((__le32 *)args);
+	*serial_number = le32_to_cpup((__le32 *)args);
 
 	return 0;
 }