mmc: mtk-sd: select REGULATOR

The mtk-sd driver requires a regulator to be present, even if it is
the "fixed" regulator.  So select REGULATOR to make it hard to build
unusable configurations.
Signed-off-by: NeilBrown <neil@brown.name>
Reviewed-by: Chaotian Jing <chaotian.jing@mediatek.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/Kconfig

@@ -941,6 +941,7 @@ config MMC_BCM2835
 config MMC_MTK
 	tristate "MediaTek SD/MMC Card Interface support"
 	depends on HAS_DMA
+	select REGULATOR
 	help
 	  This selects the MediaTek(R) Secure digital and Multimedia card Interface.
 	  If you have a machine with a integrated SD/MMC card reader, say Y or M here.