OMAP: McBSP: Fix static function warning

This patch fixes sparse warning due non declaration of static function

sound/soc/omap/omap-mcbsp.c:783:5: warning: symbol 'omap_mcbsp_st_info_volsw' was not declared. Should it be static?
Signed-off-by: NG, Manjunath Kondaiah <manjugk@ti.com>
Cc: alsa-devel@alsa-project.org
Cc: Jarkko Nikula <jhnikula@gmail.com>
Cc: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Nishanth Menon <nm@ti.com>
Acked-by: NPeter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: NJarkko Nikula <jhnikula@gmail.com>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NLiam Girdwood <lrg@slimlogic.co.uk>

sound/soc/omap/omap-mcbsp.c

@@ -759,7 +759,7 @@ static struct snd_soc_dai_driver omap_mcbsp_dai =
 	.ops = &mcbsp_dai_ops,
 };
 
-int omap_mcbsp_st_info_volsw(struct snd_kcontrol *kcontrol,
+static int omap_mcbsp_st_info_volsw(struct snd_kcontrol *kcontrol,
 			struct snd_ctl_elem_info *uinfo)
 {
 	struct soc_mixer_control *mc =