ASoC: Constify the 'driver' field of snd_soc_platform

The ASoC core does no not modify the driver of a platform. Making it const
allows ASoC platform drivers to declare the snd_soc_platform_driver struct as
const.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/sound/soc.h

@@ -371,7 +371,7 @@ int snd_soc_suspend(struct device *dev);
 int snd_soc_resume(struct device *dev);
 int snd_soc_poweroff(struct device *dev);
 int snd_soc_register_platform(struct device *dev,
-		struct snd_soc_platform_driver *platform_drv);
+		const struct snd_soc_platform_driver *platform_drv);
 void snd_soc_unregister_platform(struct device *dev);
 int snd_soc_register_codec(struct device *dev,
 		const struct snd_soc_codec_driver *codec_drv,
@@ -823,7 +823,7 @@ struct snd_soc_platform {
 	const char *name;
 	int id;
 	struct device *dev;
-	struct snd_soc_platform_driver *driver;
+	const struct snd_soc_platform_driver *driver;
 	struct mutex mutex;
 
 	unsigned int suspended:1; /* platform is suspended */

sound/soc/soc-core.c

@@ -3906,7 +3906,7 @@ EXPORT_SYMBOL_GPL(snd_soc_unregister_dais);
  * @platform: platform to register
  */
 int snd_soc_register_platform(struct device *dev,
-		struct snd_soc_platform_driver *platform_drv)
+		const struct snd_soc_platform_driver *platform_drv)
 {
 	struct snd_soc_platform *platform;