rtc: stmp3xxx: 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-stmp3xxx.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Freescale STMP37XX/STMP378X Real Time Clock driver
  *
@@ -8,15 +9,6 @@
  * Copyright 2008 Embedded Alley Solutions, Inc All Rights Reserved.
  * Copyright 2011 Wolfram Sang, Pengutronix e.K.
  */
-
-/*
- * The code contained herein is licensed under the GNU General Public
- * License. You may obtain a copy of the GNU General Public License
- * Version 2 or later at the following locations:
- *
- * http://www.opensource.org/licenses/gpl-license.html
- * http://www.gnu.org/copyleft/gpl.html
- */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/io.h>