ASoC: cache: Fix error code when not using ASoC level cache

It is not an error to have no cache so we shouldn't return an error code
and cause our callers to fail, just silently do nothing instead.  Thanks
to Jarkko for identify the problematic commit.
Reported-by: NJarkko Nikula <jarkko.nikula@linux.intel.com>
Reported-by: NFabio Estevam <festevam@gmail.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/soc-cache.c

@@ -73,7 +73,7 @@ int snd_soc_cache_init(struct snd_soc_codec *codec)
 	reg_size = codec_drv->reg_cache_size * codec_drv->reg_word_size;
 
 	if (!reg_size)
-		return -EINVAL;
+		return 0;
 
 	mutex_init(&codec->cache_rw_mutex);