ASoC: wm9081: fixup wm9081_digital_mute() reg read

commit 48c33876 ("ASoC: wm9081: replace codec to component")
replaced codec to component, but it didn't keep WM9081_DAC_DIGITAL_2
value to reg. This patch fixup it.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm9081.c

@@ -1155,7 +1155,7 @@ static int wm9081_digital_mute(struct snd_soc_dai *codec_dai, int mute)
 	struct snd_soc_component *component = codec_dai->component;
 	unsigned int reg;
 
-	snd_soc_component_read32(component, WM9081_DAC_DIGITAL_2);
+	reg = snd_soc_component_read32(component, WM9081_DAC_DIGITAL_2);
 
 	if (mute)
 		reg |= WM9081_DAC_MUTE;