mfd: wm8994: Ensure that the whole MFD is built into a single module

The MFD part of wm8994 consists of three files wm8994-core.c,
wm8994-irq.c and wm8994-regmap.c only wm8994-core.c has a
MODULE_DESCRIPTION / LICENSE. These were clearly intended to be built
as a single module, but currently are not. This will lead to a tainted
kernel when loading modules for wm8894-irq.c and wm8994-regmap.c because
are missing a license.

This patch fixes this issue by grouping the three files together into a
single module.
Reported-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Makefile

@@ -61,7 +61,8 @@ wm8350-objs			:= wm8350-core.o wm8350-regmap.o wm8350-gpio.o
 wm8350-objs			+= wm8350-irq.o
 obj-$(CONFIG_MFD_WM8350)	+= wm8350.o
 obj-$(CONFIG_MFD_WM8350_I2C)	+= wm8350-i2c.o
-obj-$(CONFIG_MFD_WM8994)	+= wm8994-core.o wm8994-irq.o wm8994-regmap.o
+wm8994-objs			:= wm8994-core.o wm8994-irq.o wm8994-regmap.o
+obj-$(CONFIG_MFD_WM8994)	+= wm8994.o
 
 obj-$(CONFIG_TPS6105X)		+= tps6105x.o
 obj-$(CONFIG_TPS65010)		+= tps65010.o