mfd: wm8400 needs to depend on I2C=y

Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

drivers/mfd/Kconfig

@@ -479,7 +479,7 @@ config MFD_S5M_CORE
 config MFD_WM8400
 	bool "Support Wolfson Microelectronics WM8400"
 	select MFD_CORE
-	depends on I2C
+	depends on I2C=y
 	select REGMAP_I2C
 	help
 	  Support for the Wolfson Microelecronics WM8400 PMIC and audio