ASoC: core: fix possible ZERO_SIZE_PTR pointer dereferencing error.

commit 6596aa04 upstream.

Since we cannot make sure the 'params->num_regs' will always be none
zero here, and then if it equals to zero, the kmemdup() will return
ZERO_SIZE_PTR, which equals to ((void *)16).

So this patch fix this with just doing the zero check before calling
kmemdup().
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
[ kamal: backport to 3.13-stable: context ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

sound/soc/soc-core.c

@@ -3236,7 +3236,7 @@ int snd_soc_bytes_put(struct snd_kcontrol *kcontrol,
 	unsigned int val;
 	void *data;
 
-	if (!codec->using_regmap)
+	if (!codec->using_regmap || !params->num_regs)
 		return -EINVAL;
 
 	len = params->num_regs * codec->val_bytes;