mmc: sdhci-esdhc-imx: fix mmc ddr mode regression issue

It's caused by the platform driver was still using MMC_TIMING_UHS_DDR50
for MMC DDR mode which needs update too.

Reported-by: Fabio Estevam <fabio.estevam@freescale.com>
Reported-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Dong Aisheng <b29396@freescale.com>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
[Ulf Hansson] Resolved conflict
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>