mmc: card: Call blk_requeue_request() with queue-lock held

blk_requeue_request() must be called with queue lock held.

If it is called without this lock then there is a chance that block-
queue would be accessed simultaneously by more than one entity (sat
request completion & re-queue) and both can mess-up the queue
pointers which can result in unexpected results.

Change-Id: If81711ecf65a185f4c8dc19b8568621460c93db8
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>