block: use bdev_alignment_offset in part_alignment_offset_show

Replace the open coded offset calculation with the proper helper.
This is an ABI change in that the -1 for a misaligned partition is
properly propagated, which can be considered a bug fix and matches
what is done on the whole device.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMartin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220415045258.199825-17-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

block/partitions/core.c

@@ -200,11 +200,7 @@ static ssize_t part_ro_show(struct device *dev,
 static ssize_t part_alignment_offset_show(struct device *dev,
 					  struct device_attribute *attr, char *buf)
 {
-	struct block_device *bdev = dev_to_bdev(dev);
-
-	return sprintf(buf, "%u\n",
-		queue_limit_alignment_offset(&bdev_get_queue(bdev)->limits,
-				bdev->bd_start_sect));
+	return sprintf(buf, "%u\n", bdev_alignment_offset(dev_to_bdev(dev)));
 }
 
 static ssize_t part_discard_alignment_show(struct device *dev,