mfd: Register WM8400 codec device

Register a child device for the codec in the WM8400.

Also switch the unregistration of the MFD devices to use the MFD core
since the current code is hand rolling the same thing.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 8cd3dd9..ddfb12b 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -116,6 +116,7 @@
 
 config MFD_WM8400
 	tristate "Support Wolfson Microelectronics WM8400"
+	select MFD_CORE
 	depends on I2C
 	help
 	  Support for the Wolfson Microelecronics WM8400 PMIC and audio