spi: spi-fsl-dspi: Switch to SPDX identifier

Adopt the SPDX license identifier headers to ease license compliance
management.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

-/*
- * drivers/spi/spi-fsl-dspi.c
- *
- * Copyright 2013 Freescale Semiconductor, Inc.
- *
- * Freescale DSPI driver
- * This file contains a driver for the Freescale DSPI
- *
- * 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.
- *
- */
+// SPDX-License-Identifier: GPL-2.0+
+//
+// Copyright 2013 Freescale Semiconductor, Inc.
+//
+// Freescale DSPI driver
+// This file contains a driver for the Freescale DSPI
 
 #include <linux/clk.h>
 #include <linux/delay.h>