mmc: block: Fix issues with mmc ioctl path on 4.14 kernel

On latest kernels, mmc IOCTL commands won't be issued to the driver
directly. Instead, they would be issued through the block layer as
drv_op requests. mmc-cmdq thread process them just like regular
requests by fetching from block layer.

MMC IOCTL commands are getting issued by putting cmdq in halt state.
But when cmdq is in the halt state, cmdq thread won't fetch the
requests until it gets un-halted by other entity (say runtime suspend/
resume). This will result in a delay in processing IOCTL and IO
requests.

Since cmdq thread takes care of halting cq engine when it finds a
drv_op request, no need to halt cmdq anymore in IOCTL path.
It will fix the issue with IOCTL path.

Change-Id: I6636870ddb3f07f594c63045f64821681caaa3ad
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>