mmc: sdhci-msm: Boost controller core clock

Ensure SDCC is working with maximum clock otherwise card
detection could be extremely slow, up to 7 seconds.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Reviewed-by: Georgi Djakov <georgi.djakov@linaro.org>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>