ASoC: madera: Update SPDX headers

The madera driver was merged too late to catch Thomas Gleixner's cleanup
of the SPDX headers tree wide. Update the headers to match what was done
in that patch.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/sound/madera-pdata.h

@@ -1,13 +1,9 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * Platform data for Madera codec driver
  *
  * Copyright (C) 2016-2019 Cirrus Logic, Inc. and
  *                         Cirrus Logic International Semiconductor Ltd.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #ifndef MADERA_CODEC_PDATA_H