ASoC: mediatek: mt6359: 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/20230307040938.7484-5-trevor.wu@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/mt6359.c

@@ -358,7 +358,7 @@ static int mt6359_put_volsw(struct snd_kcontrol *kcontrol,
 	struct mt6359_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 index = ucontrol->value.integer.value[0];
 	int ret;