ASoC: Fix WM8994 dependency

The dependency on MFD_WM8994 rather than I2C went awry.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>

sound/soc/codecs/Kconfig

@@ -61,7 +61,7 @@ config SND_SOC_ALL_CODECS
 	select SND_SOC_WM8988 if SND_SOC_I2C_AND_SPI
 	select SND_SOC_WM8990 if I2C
 	select SND_SOC_WM8993 if I2C
-	select SND_SOC_WM8994 if I2C
+	select SND_SOC_WM8994 if MFD_WM8994
 	select SND_SOC_WM9081 if I2C
 	select SND_SOC_WM9705 if SND_SOC_AC97_BUS
 	select SND_SOC_WM9712 if SND_SOC_AC97_BUS