mmc: dw_mmc: exynos: Revert the sdr_timing assignment

e6c784eded7b3 ("mmc: dw_mmc: exynos: move the exynos private init") was
wrongly assigning ddr_timing value to sdr_timing. This patch fixes this
by reverting the sdr_timing assignment statement to the earlier location.

Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@samsung.com>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>