drivers: power: supply: goldfish_battery: Put an SPDX tag

There was a checkpatch complain:

"Missing or malformed SPDX-License-Identifier tag".
Signed-off-by: NRoman Kiryanov <rkir@google.com>
Signed-off-by: NSebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/goldfish_battery.c

+// SPDX-License-Identifier: GPL
 /*
  * Power supply driver for the goldfish emulator
  *
@@ -5,15 +6,6 @@
  * Copyright (C) 2012 Intel, Inc.
  * Copyright (C) 2013 Intel, Inc.
  * Author: Mike Lockwood <lockwood@android.com>
- *
- * 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/module.h>