Input: imx_keypad - switch to SPDX identifier

Adopt the SPDX license identifier headers to ease license compliance
management.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/keyboard/imx_keypad.c

-/*
- * Driver for the IMX keypad port.
- * Copyright (C) 2009 Alberto Panizzo <maramaopercheseimorto@gmail.com>
- *
- * 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.
- */
+// SPDX-License-Identifier: GPL-2.0
+//
+// Driver for the IMX keypad port.
+// Copyright (C) 2009 Alberto Panizzo <maramaopercheseimorto@gmail.com>
 
 #include <linux/clk.h>
 #include <linux/delay.h>