rtc: rv8803: 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-rv8803.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * RTC driver for the Micro Crystal RV8803
  *
  * Copyright (C) 2015 Micro Crystal SA
- *
  * Alexandre Belloni <alexandre.belloni@free-electrons.com>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/bcd.h>