ASoC: wm8996: Fix negative array index read

Spotted by coverity CID 146355.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/codecs/wm8996.c

@@ -438,6 +438,8 @@ static int wm8996_get_retune_mobile_enum(struct snd_kcontrol *kcontrol,
 	struct wm8996_priv *wm8996 = snd_soc_codec_get_drvdata(codec);
 	int block = wm8996_get_retune_mobile_block(kcontrol->id.name);
 
+	if (block < 0)
+		return block;
 	ucontrol->value.enumerated.item[0] = wm8996->retune_mobile_cfg[block];
 
 	return 0;