rtc: ab3100: convert to SPDX identifier

Use SPDX-License-Identifier instead of the custom license line.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-ab3100.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007-2009 ST-Ericsson AB
- * License terms: GNU General Public License (GPL) version 2
  * RTC clock driver for the AB3100 Analog Baseband Chip
  * Author: Linus Walleij <linus.walleij@stericsson.com>
  */