mmc: sdhci-esdhc-imx: fix strobe DLL lock wrong clock issue

When enable DDR, the clock factor definition is changed.
e.g. original 200Mhz will become 100Mhz once MIX_CTRL_DDREN bit is set
So we need to update the clock setting then the strobe dll can lock
the correct clock rate.

Additionally we also need disable the clock before locking strobe dll.

Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>