UHS_REG should be cleared for non-DDR mode. But currently there is
no way to clear DDR mode, if it is already set once. This patch adds
clearing DDR mode for non-DDR mode.
Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com> Acked-by: Will Newton <will.newton@imgtec.com> Signed-off-by: Chris Ball <cjb@laptop.org>