mmc: sdhci: Fix unclocked access during MMC_POWER_UP

During MMC_POWER_UP the clocks are turned off when enabling power
to the card. Make sure the controller clocks are enabled for
normal register access.

Change-Id: Iad6fc4dfc6e44d0a609b66432b0985d589c3e5b9
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>