ASoC: rt5640: Staticize hp_amp_power_on

'hp_amp_power_on' is used only in this file. Make it static.
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/codecs/rt5640.c

@@ -926,7 +926,7 @@ static int rt5640_set_dmic2_event(struct snd_soc_dapm_widget *w,
 	return 0;
 }
 
-void hp_amp_power_on(struct snd_soc_codec *codec)
+static void hp_amp_power_on(struct snd_soc_codec *codec)
 {
 	struct rt5640_priv *rt5640 = snd_soc_codec_get_drvdata(codec);