mmc: sdhci-omap: Invoke sdhci_get_of_property to read sdhci dt properties

Invoke sdhci_get_of_property defined in sdhci-pltfm.c to read
sdhci specific properties from dt node.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>