ASoC: Constify the 'compr_ops' field of snd_soc_platform_driver

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

@@ -804,7 +804,7 @@ struct snd_soc_platform_driver {
 	const struct snd_pcm_ops *ops;
 
 	/* platform stream compress ops */
-	struct snd_compr_ops *compr_ops;
+	const struct snd_compr_ops *compr_ops;
 
 	/* platform stream completion event */
 	int (*stream_event)(struct snd_soc_dapm_context *dapm, int event);