mmc: sdhci-esdhci-imx: disable DLL delay line settings explicitly

Disable DLL delay line settings explicitly during driver initialization
in case ROM/uBoot had set an invalid delay.
e.g. MX6DL ROM has set the default delay line(DLLCTRL) to 0x1000021,
the uSDHC clock timing will become marginal when works on DDR mode
due to default delay and will possibly see CRC errors in case the board
is not perfectly designed on the eMMC chip layout.

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>