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>

sound/soc/intel/common/soc-acpi-intel-cml-match.c

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * soc-acpi-intel-cml-match.c - tables and support for CML ACPI enumeration.
  *