ASoC: Fix soc-cache buffer overflow bug

Make sure we stay within the cache boundaries when updating the
register cache.
Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/soc-cache.c

@@ -203,8 +203,9 @@ static int snd_soc_8_16_write(struct snd_soc_codec *codec, unsigned int reg,
 	data[1] = (value >> 8) & 0xff;
 	data[2] = value & 0xff;
 
-	if (!snd_soc_codec_volatile_register(codec, reg))
-		reg_cache[reg] = value;
+	if (!snd_soc_codec_volatile_register(codec, reg)
+		&& reg < codec->driver->reg_cache_size)
+			reg_cache[reg] = value;
 
 	if (codec->cache_only) {
 		codec->cache_sync = 1;