target: fix discard alignment on partitions

Use the proper bdev_discard_alignment helper that accounts for partition
offsets.

Fixes: c66ac9db ("[SCSI] target: Add LIO target core v4.0.0-rc6")
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/20220415045258.199825-4-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/target/target_core_device.c

@@ -849,8 +849,8 @@ bool target_configure_unmap_from_queue(struct se_dev_attrib *attrib,
 	 */
 	attrib->max_unmap_block_desc_count = 1;
 	attrib->unmap_granularity = q->limits.discard_granularity / block_size;
-	attrib->unmap_granularity_alignment = q->limits.discard_alignment /
-								block_size;
+	attrib->unmap_granularity_alignment =
+		bdev_discard_alignment(bdev) / block_size;
 	return true;
 }
 EXPORT_SYMBOL(target_configure_unmap_from_queue);