FROMGIT: block: mq-deadline: Track the dispatch position

Track the position (sector_t) of the most recently dispatched request
instead of tracking a pointer to the next request to dispatch. This
patch is the basis for patch "Handle requeued requests correctly".
Without this patch it would be significantly more complicated to make
sure that zoned writes are dispatched in LBA order per zone.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Cc: Ming Lei <ming.lei@redhat.com>
Change-Id: I7ea38c43ae4e80b3a2257b631b58754c60aff4df
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-10-bvanassche@acm.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Bug: 275581839
(cherry picked from commit 83c46ed6 https://git.kernel.dk/cgit/linux/

)
Signed-off-by: Bart Van Assche <bvanassche@google.com>