ASoC: rt5640: Remove the unused field in private data

The patch removes the unused field in private data.
Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/codecs/rt5640.h

@@ -2095,7 +2095,6 @@ struct rt5640_priv {
 	int pll_in;
 	int pll_out;
 
-	int dmic_en;
 	bool hp_mute;
 };