gpio: pcie-idio-24: Prune superfluous license boilerplate

The SPDX License Identifier line renders the GPL boilerplate text
superfluous, so let's remove it.

Signed-off-by: William Breathitt Gray <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-pcie-idio-24.c

···
  * GPIO driver for the ACCES PCIe-IDIO-24 family
  * Copyright (C) 2018 William Breathitt Gray
  *
- * 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 in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
  * This driver supports the following ACCES devices: PCIe-IDIO-24,
  * PCIe-IDI-24, PCIe-IDO-24, and PCIe-IDIO-12.
  */