MMC master clock rate can vary for each instance of the MMC controller
on the device. Use clk_get_rate instead to get the value.
Signed-off-by: NBalaji TK  <balajitk@ti.com>
Reviewed-by: NVenkatraman S <svenkatr@ti.com>
Tested-by: NHebbar, Gururaja <gururaja.hebbar@ti.com>
Acked-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: NChris Ball <cjb@laptop.org>