mmc: core: Ensure clocks are always enabled before host interaction

Ensure clocks are always enabled before any interaction with the
host controller driver. This makes sure that there is no race
between host execution and the core layer turning off clocks
in different context with clock gating framework.

CRs-Fixed: 324380
Change-Id: Id3dc2074ed81bf758649bc61ce918500a95e9bae
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>