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/atom/Makefile

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: GPL-2.0
+# SPDX-License-Identifier: GPL-2.0-only
 snd-soc-sst-atom-hifi2-platform-objs :=	sst-mfld-platform-pcm.o \
 					sst-mfld-platform-compress.o \
 					sst-atom-controls.o

sound/soc/intel/atom/sst/Makefile

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: GPL-2.0
+# SPDX-License-Identifier: GPL-2.0-only
 snd-intel-sst-core-objs := sst.o sst_ipc.o sst_stream.o sst_drv_interface.o sst_loader.o sst_pvt.o
 snd-intel-sst-pci-objs += sst_pci.o
 snd-intel-sst-acpi-objs += sst_acpi.o