mmc: core: Add clock hold and release pair for cmdq_ops

mmc_host_clk_hold/release pair should be added for relevant
cmdq_ops. Since it enables host->clock which is needed
for register access as well (apart from
MCLK).

Change-Id: I6d9d15a421225c5b4179cb19e467a17d01ad176f
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Signed-off-by: Talel Shenhar <tatias@codeaurora.org>