staging: rtl8712: replace licence header with SPDX licence id

fixed warning found by checkpatch
Signed-off-by: André Lehmann <lenneman@web.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/hal_init.c

+// SPDX-License-Identifier: GPL-2.0
 /******************************************************************************
  * hal_init.c
  *
  * Copyright(c) 2007 - 2010 Realtek Corporation. All rights reserved.
  * Linux device driver for RTL8192SU
  *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of version 2 of the GNU General Public License 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.
- *
  * Modifications for inclusion into the Linux staging tree are
  * Copyright(c) 2010 Larry Finger. All rights reserved.
  *