mmc: host: Ensure mmc resume while controlling clock scaling from sysfs

Ensure that MMC/SD card is runtime resumed while enabling or disabling
clock scaling from sysfs. This is needed because the tuning commands
might fail if the card is runtime suspended.

Change-Id: I03767a9ceda2c424f0ce939b8db309d7e81a71da
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>