blk-mq: don't pass **hctx to blk_mq_mark_tag_wait()

'hctx' won't be changed at all, so not necessary to pass
'**hctx' to blk_mq_mark_tag_wait().

Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Tested-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>