ASoC: SOF/Intel: clarify SPDX license with GPL-2.0-only

Remove the ambiguity with GPL-2.0 and use an explicit GPL-2.0-only
tag.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Link: https://lore.kernel.org/r/20200501145850.15178-1-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/include/sound/sof/dai.h b/include/sound/sof/dai.h
index 2565edd..34f135a 100644
--- a/include/sound/sof/dai.h
+++ b/include/sound/sof/dai.h
@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause) */
 /*
  * This file is provided under a dual BSD/GPLv2 license.  When using or
  * redistributing this file, you may do so under either license.