rtc: goldfish: convert to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-goldfish.c

+// SPDX-License-Identifier: GPL-2.0
 /* drivers/rtc/rtc-goldfish.c
  *
  * Copyright (C) 2007 Google, Inc.
  * Copyright (C) 2017 Imagination Technologies Ltd.
- *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * 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/io.h>