mmc: omap_hsmmc: Fix UHS card with DDR50 support

The commit, mmc: omap: clarify DDR timing mode between SD-UHS and eMMC,
switched omap_hsmmc to support MMC DDR mode instead of UHS DDR50 mode.

Add UHS DDR50 mode again and this time let's also keep the MMC DDR mode.

Fixes: 5438ad95 (mmc: omap: clarify DDR timing mode between SD-UHS and eMMC)
Reported-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>