dm table: fix blk_stack_limits arg to use bytes not sectors

The offset passed to blk_stack_limits() must be in bytes not sectors.
Fixes false warnings like the following:
device-mapper: table: 254:1: target device sda6 is misaligned
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Reported-by: Frans Pop <elendil@planet.nl>
Tested-by: Frans Pop <elendil@planet.nl>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-table.c

@@ -495,7 +495,7 @@ int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
 		return 0;
 	}
 
-	if (blk_stack_limits(limits, &q->limits, start) < 0)
+	if (blk_stack_limits(limits, &q->limits, start << 9) < 0)
 		DMWARN("%s: target device %s is misaligned",
 		       dm_device_name(ti->table->md), bdevname(bdev, b));