mmc: sdhci-of-esdhc: poll ESDHC_CLOCK_STABLE bit with udelay

The loop to poll ESDHC_CLOCK_STABLE bit with mdelay would waste time
because the time to stabilize is much less than 1 ms. This patch is
to use udelay instead to avoid time wasting.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>