mfd: Hook WM831x into build system

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index 6f8a9a1af..285cb32 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -15,6 +15,8 @@
 obj-$(CONFIG_MFD_TC6393XB)	+= tc6393xb.o
 
 obj-$(CONFIG_MFD_WM8400)	+= wm8400-core.o
+wm831x-objs			:= wm831x-core.o wm831x-irq.o wm831x-otp.o
+obj-$(CONFIG_MFD_WM831X)	+= wm831x.o
 wm8350-objs			:= wm8350-core.o wm8350-regmap.o wm8350-gpio.o
 obj-$(CONFIG_MFD_WM8350)	+= wm8350.o
 obj-$(CONFIG_MFD_WM8350_I2C)	+= wm8350-i2c.o