ASoC: cache: Fix possible ZERO_SIZE_PTR pointer dereferencing error.

Since we cannot make sure the 'reg_size' will always be none zero here,
and then if 'reg_size' equals to zero, the kzalloc() will return ZERO_SIZE_PTR,
which equals to ((void *)16).

So this patch fix this with just doing the 'reg_size' zero check before calling
kzalloc().

Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/soc-cache.c

@@ -72,6 +72,9 @@ 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;
+
 	mutex_init(&codec->cache_rw_mutex);
 
 	dev_dbg(codec->dev, "ASoC: Initializing cache for %s codec\n",