can: kvaser_usb: Add SPDX GPL-2.0 license identifier

Add SPDX GPL-2.0 license identifier to kvaser_usb.c.
Signed-off-by: Jimmy Assarsson <extja@kvaser.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/kvaser_usb.c

-/*
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License as
- * published by the Free Software Foundation version 2.
- *
- * Parts of this driver are based on the following:
+// SPDX-License-Identifier: GPL-2.0
+/* Parts of this driver are based on the following:
  *  - Kvaser linux leaf driver (version 4.78)
  *  - CAN driver for esd CAN-USB/2
  *  - Kvaser linux usbcanII driver (version 5.3)