ASoC: mediatek: mt6358: fix UNINIT problem

Coverity shows decaring variable reg without initializer. When
regmap_read returns an error, reg keeps the value left from earlier
computation. To prevent from the unexpected result in the case, assign
0 to reg.
Signed-off-by: Trevor Wu <trevor.wu@mediatek.com>
Link: https://lore.kernel.org/r/20230307040938.7484-4-trevor.wu@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/mt6358.c

@@ -429,7 +429,7 @@ static int mt6358_put_volsw(struct snd_kcontrol *kcontrol,
 	struct mt6358_priv *priv = snd_soc_component_get_drvdata(component);
 	struct soc_mixer_control *mc =
 			(struct soc_mixer_control *)kcontrol->private_value;
-	unsigned int reg;
+	unsigned int reg = 0;
 	int ret;
 
 	ret = snd_soc_put_volsw(kcontrol, ucontrol);