platform/x86: intel-vbtn: Replace License by SDPX identifier

Replace License short header by SPDX identifier.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: NDarren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/intel-vbtn.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  *  Intel Virtual Button driver for Windows 8.1+
  *
  *  Copyright (C) 2016 AceLan Kao <acelan.kao@canonical.com>
  *  Copyright (C) 2016 Alex Hung <alex.hung@canonical.com>
- *
- *  This program is free software; you can redistribute it and/or modify
- *  it under the terms of the GNU General Public License as published by
- *  the Free Software Foundation; either version 2 of the License, or
- *  (at your option) any later version.
- *
- *  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/acpi.h>