Two cases:

1) blk_mq_alloc_request() needlessly re-runs the queue, after
   calling into the tag allocation without NOWAIT set. We don't
   need to do that.

2) blk_mq_map_request() should just use blk_mq_run_hw_queue() with
   the async flag set to false.
Signed-off-by: NJens Axboe <axboe@fb.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>