Input: cpcap-pwrbutton - replace GPLv2 boilerplate with SPDX

Replace the GPLv2 boilerplate text with a nice and short
SPDX header.

Signed-off-by: Sebastian Reichel <sre@kernel.org>
Link: https://lore.kernel.org/r/20230705212231.631525-1-sre@kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: sre

drivers/input/misc/cpcap-pwrbutton.c

@@ -1,16 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * CPCAP Power Button Input Driver
  *
  * Copyright (C) 2017 Sebastian Reichel <sre@kernel.org>
- *
- * This file is subject to the terms and conditions of the GNU General
- * Public License. See the file "COPYING" in the main directory of this
- * archive for more details.
- *
- * 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.
  */
 
 #include <linux/module.h>