mmc: sdhci-spear: Simplify by adding build dependency to CONFIG_OF

This driver is used on SoCs which are using CONFIG_OF. By adding a
compile dependency in the Kconfig, it enables us to simplify some code.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 2f850ac..7f4db90 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -255,6 +255,7 @@
 config MMC_SDHCI_SPEAR
 	tristate "SDHCI support on ST SPEAr platform"
 	depends on MMC_SDHCI && PLAT_SPEAR
+	depends on OF
 	help
 	  This selects the Secure Digital Host Controller Interface (SDHCI)
 	  often referrered to as the HSMMC block in some of the ST SPEAR range