mmc: core: Hold clocks along with runtime get of class device

In mmc_claim_host, we are runtime resuming the class device and the
platform device. The platform device is allowed to runtime suspend
only after mmc_host gets released. So along with doing
runtime get/put of platform device, hold/release the clocks. This will
ensure that the clock gating work will not get frequently scheduled and
cancelled. Also the clock gating will now not kick in during runtime
resume of the platform.

Change-Id: I6b62839c7704fd85874709d53105d97a359395ab
Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>