mmc: sdhci-of-esdhc: convert to use esdhc_tuning_window_ptr()

Convert to use a new function esdhc_tuning_window_ptr() to
get tuning window start point and end point.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20191212075219.48625-1-yangbo.lu@nxp.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>