ASoC: Constify the 'ops' field of snd_soc_platform_driver

The ASoC core does not modify a platform driver's ops structure. Making it const
allows ASoC platform drivers to declare their snd_pcm_ops 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

@@ -801,7 +801,7 @@ struct snd_soc_platform_driver {
 		struct snd_soc_dai *);
 
 	/* platform stream pcm ops */
-	struct snd_pcm_ops *ops;
+	const struct snd_pcm_ops *ops;
 
 	/* platform stream compress ops */
 	struct snd_compr_ops *compr_ops;