rtc: at91sam9: convert to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-at91sam9.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * "RTT as Real Time Clock" driver for AT91SAM9 SoC family
  *
  * (C) 2007 Michel Benoit
  *
  * Based on rtc-at91rm9200.c by Rick Bronson
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version
- * 2 of the License, or (at your option) any later version.
  */
 
 #include <linux/clk.h>