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>
diff --git a/sound/soc/codecs/twl4030.c b/sound/soc/codecs/twl4030.c
index a5062cc..4275eea 100644
--- a/sound/soc/codecs/twl4030.c
+++ b/sound/soc/codecs/twl4030.c
@@ -924,7 +924,7 @@
 			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);