Input: imx_keypad - switch to SPDX identifier

Adopt the SPDX license identifier headers to ease license compliance
management.

Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/keyboard/imx_keypad.c

···
-/*
- * Driver for the IMX keypad port.
- * Copyright (C) 2009 Alberto Panizzo <[e-mail]>
- *
- * 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 <[e-mail]>
 
 #include <linux/clk.h>
 #include <linux/delay.h>