mfd: max77686: Allow driver to be built as a module

The driver's Kconfig symbol is a boolean but nothing prevents the driver
to be built as a module instead of built-in. It is true that most system
integrators will choose the latter but the config should not restrict it.
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -528,8 +528,8 @@ config MFD_MAX14577
 	  of the device.
 
 config MFD_MAX77686
-	bool "Maxim Semiconductor MAX77686/802 PMIC Support"
-	depends on I2C=y
+	tristate "Maxim Semiconductor MAX77686/802 PMIC Support"
+	depends on I2C
 	depends on OF
 	select MFD_CORE
 	select REGMAP_I2C