rtc: au1xxx: convert to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text.
Signed-off-by: NNobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210707075804.337458-2-nobuhiro1.iwamatsu@toshiba.co.jp

drivers/rtc/rtc-au1xxx.c

+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Au1xxx counter0 (aka Time-Of-Year counter) RTC interface driver.
  *
  * Copyright (C) 2008 Manuel Lauss <mano@roarinelk.homelinux.net>
- *
- * This file is subject to the terms and conditions of the GNU General Public
- * License.  See the file "COPYING" in the main directory of this archive
- * for more details.
  */
 
 /* All current Au1xxx SoCs have 2 counters fed by an external 32.768 kHz