gpio: ts4900: Use SPDX header

Remove boilerplate, use the SPDX license identifier.
Signed-off-by: Kris Bahnsen <kris@embeddedTS.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

drivers/gpio/gpio-ts4900.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Digital I/O driver for Technologic Systems I2C FPGA Core
  *
  * Copyright (C) 2015 Technologic Systems
  * Copyright (C) 2016 Savoir-Faire Linux
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
- * This program is distributed "as is" WITHOUT ANY WARRANTY of any
- * kind, whether expressed or implied; without even the implied warranty
- * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License version 2 for more details.
  */
 
 #include <linux/gpio/driver.h>