mmc: core: Attribute the IO wait time properly in mmc_wait_for_req_done()

In mmc_wait_for_req_done() function, change the call wait_for_completion()
to wait_for_compltion_io(). This change makes the kernel account for
wait time as I/O wait and through another configuration, this io wait
is treated as busy which makes the acpu clock to scale up.

Change-Id: Iebdc7b1b22871bf845f10a55e2272816c72d9964
Signed-off-by: Murali Palnati <palnatim@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>