dm: open code blk_max_size_offset in max_io_len

max_io_len always passes an explicitly non-zero chunk_sectors into
blk_max_size_offset.  That means much of blk_max_size_offset is not
needed and can be open coded to simplify the code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/r/20220614090934.570632-3-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/dm.c

@@ -1086,23 +1086,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)
 {
 	sector_t target_offset = dm_target_offset(ti, sector);
 	sector_t len = max_io_len_target_boundary(ti, target_offset);
-	sector_t max_len;
 
 	/*
 	 * Does the target need to split IO even further?
 	 * - varied (per target) IO splitting is a tenet of DM; this
 	 *   explains why stacked chunk_sectors based splitting via
-	 *   blk_max_size_offset() isn't possible here. So pass in
-	 *   ti->max_io_len to override stacked chunk_sectors.
+	 *   blk_queue_split() isn't possible here.
 	 */
-	if (ti->max_io_len) {
-		max_len = blk_max_size_offset(ti->table->md->queue,
-					      target_offset, ti->max_io_len);
-		if (len > max_len)
-			len = max_len;
-	}
-
-	return len;
+	if (!ti->max_io_len)
+		return len;
+	return min_t(sector_t, len,
+		min(queue_max_sectors(ti->table->md->queue),
+		    blk_chunk_sectors_left(target_offset, ti->max_io_len)));
 }
 
 int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)