ASoC: SOF: imx: add missing MODULE_LICENSE() for imx-common

Fix build warning:
WARNING: modpost: missing MODULE_LICENSE() in sound/soc/sof/imx/imx-common.o

Fixes: 18ebffe4 ("ASoC: SOF: imx: Add debug support for imx platforms")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@gmail.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200921104746.2903507-1-kai.vehmanen@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/imx/imx-common.c

@@ -4,6 +4,7 @@
 //
 // Common helpers for the audio DSP on i.MX8
 
+#include <linux/module.h>
 #include <sound/sof/xtensa.h>
 #include "../ops.h"
 
@@ -70,3 +71,5 @@ void imx8_dump(struct snd_sof_dev *sdev, u32 flags)
 			   IMX8_STACK_DUMP_SIZE);
 }
 EXPORT_SYMBOL(imx8_dump);
+
+MODULE_LICENSE("Dual BSD/GPL");