ASoC: Staticise put_twl4030_opmode_enum_double()

It's an operation for a control and doesn't need to be exported.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/twl4030.c

@@ -924,7 +924,7 @@ static const struct soc_enum twl4030_op_modes_enum =
 			ARRAY_SIZE(twl4030_op_modes_texts),
 			twl4030_op_modes_texts);
 
-int snd_soc_put_twl4030_opmode_enum_double(struct snd_kcontrol *kcontrol,
+static int snd_soc_put_twl4030_opmode_enum_double(struct snd_kcontrol *kcontrol,
 	struct snd_ctl_elem_value *ucontrol)
 {
 	struct snd_soc_codec *codec = snd_kcontrol_chip(kcontrol);