ASoC: fsl: imx-audmux: Fix sparse warning

Fix the following sparse warning:

sound/soc/fsl/imx-audmux.c:182:3: warning: symbol 'audmux_type' was not declared. Should it be static?

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/sound/soc/fsl/imx-audmux.c b/sound/soc/fsl/imx-audmux.c
index 251f4d9..fab912e 100644
--- a/sound/soc/fsl/imx-audmux.c
+++ b/sound/soc/fsl/imx-audmux.c
@@ -176,7 +176,7 @@
 }
 #endif
 
-enum imx_audmux_type {
+static enum imx_audmux_type {
 	IMX21_AUDMUX,
 	IMX31_AUDMUX,
 } audmux_type;