mfd: mp2629: Select MFD_CORE to fix build error

MFD_MP2629 should select MFD_CORE to a prevent build error:

ERROR: modpost: "devm_mfd_add_devices" [drivers/mfd/mp2629.ko] undefined!

Fixes: 06081646 ("mfd: mp2629: Add support for mps battery charger")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -465,6 +465,7 @@ config MFD_MP2629
 	tristate "Monolithic Power Systems MP2629 ADC and Battery charger"
 	depends on I2C
 	select REGMAP_I2C
+	select MFD_CORE
 	help
 	  Select this option to enable support for Monolithic Power Systems
 	  battery charger. This provides ADC, thermal and battery charger power