rtc: sh: convert to SPDX identifiers

This patch updates license to use SPDX-License-Identifier
instead of verbose license text.

As original license mentioned, it is GPL-2.0 in SPDX.
Then, MODULE_LICENSE() should be "GPL v2" instead of "GPL".
See ${LINUX}/include/linux/module.h

	"GPL"		[GNU Public License v2 or later]
	"GPL v2"	[GNU Public License v2]
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-sh.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * SuperH On-Chip RTC Support
  *
@@ -9,10 +10,6 @@
  *
  *  Copyright (C) 2000  Philipp Rumpf <prumpf@tux.org>
  *  Copyright (C) 1999  Tetsuya Okada & Niibe Yutaka
- *
- * 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.
  */
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
@@ -681,5 +678,5 @@ MODULE_DESCRIPTION("SuperH on-chip RTC driver");
 MODULE_AUTHOR("Paul Mundt <lethal@linux-sh.org>, "
 	      "Jamie Lenehan <lenehan@twibble.org>, "
 	      "Angelo Castello <angelo.castello@st.com>");
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("GPL v2");
 MODULE_ALIAS("platform:" DRV_NAME);