ASoC: soc-core: Add support for NULL default register caches

The infrastructure for handling NULL default register maps is already
included in the soc-cache code, just ensure that we don't try to dereference
a NULL pointer while accessing a NULL register cache.
Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Acked-by: Timur Tabi <timur@freescale.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/soc-core.c

@@ -3507,6 +3507,7 @@ int snd_soc_register_codec(struct device *dev,
 		 * kernel might have freed the array by the time we initialize
 		 * the cache.
 		 */
+		if (codec_drv->reg_cache_default) {
 			codec->reg_def_copy = kmemdup(codec_drv->reg_cache_default,
 						      reg_size, GFP_KERNEL);
 			if (!codec->reg_def_copy) {
@@ -3514,6 +3515,7 @@ int snd_soc_register_codec(struct device *dev,
 				goto fail;
 			}
 		}
+	}
 
 	for (i = 0; i < num_dai; i++) {
 		fixup_codec_formats(&dai_drv[i].playback);