mmc: mediatek: depend on COMMON_CLK to fix compile tests

The MFD_OMAP_USB_HOST uses Common Clock Framework thus it cannot be
built on platforms without it (e.g. compile test on MIPS with LANTIQ):

    mips-linux-ld: drivers/mmc/host/mtk-sd.o: in function `msdc_ops_set_ios':
    mtk-sd.c:(.text+0x2bbc): undefined reference to `clk_get_parent'

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201122120056.100045-1-krzk@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/Kconfig

@@ -1023,6 +1023,7 @@ config MMC_BCM2835
 config MMC_MTK
 	tristate "MediaTek SD/MMC Card Interface support"
 	depends on HAS_DMA
+	depends on COMMON_CLK
 	select REGULATOR
 	select MMC_CQHCI
 	help