mfd: wm831x: Don't forward declare enum wm831x_auxadc

We can't forward declare enums.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/include/linux/mfd/wm831x/auxadc.h b/include/linux/mfd/wm831x/auxadc.h
index b132067..867aa23 100644
--- a/include/linux/mfd/wm831x/auxadc.h
+++ b/include/linux/mfd/wm831x/auxadc.h
@@ -15,6 +15,8 @@
 #ifndef __MFD_WM831X_AUXADC_H__
 #define __MFD_WM831X_AUXADC_H__
 
+struct wm831x;
+
 /*
  * R16429 (0x402D) - AuxADC Data
  */