mfd: wm8994: Allow modular build

The interfaces that used to be built in only (interrupts IIRC) no longer
are so allow the driver to be built as a module fixing arm64 allmodconfig
builds.
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -1243,11 +1243,11 @@ config MFD_WM8350_I2C
 	  selected to enable support for the functionality of the chip.
 
 config MFD_WM8994
-	bool "Wolfson Microelectronics WM8994"
+	tristate "Wolfson Microelectronics WM8994"
 	select MFD_CORE
 	select REGMAP_I2C
 	select REGMAP_IRQ
-	depends on I2C=y
+	depends on I2C
 	help
 	  The WM8994 is a highly integrated hi-fi CODEC designed for
 	  smartphone applicatiosn.  As well as audio functionality it