mmc: sdhci-msm: Add get_min_clock() and get_max_clock() callback

This add get_min_clock() and get_max_clock() callback
for sdhci-msm. sdhci-msm min/max clocks may be different
hence implement these callbacks.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>