rtc: pic32: 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-pic32.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * PIC32 RTC driver
  *
  * Joshua Henderson <joshua.henderson@microchip.com>
  * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
  *
- * 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.
- *
- * This program is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
- * more details.
  */
 #include <linux/init.h>
 #include <linux/module.h>