block: dasd_genhd: convert to blkdev_reread_part

Also remove the obsolete comment.
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Tested-by: NJarod Wilson <jarod@redhat.com>
Acked-by: NJarod Wilson <jarod@redhat.com>
Acked-by: NSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/s390/block/dasd_genhd.c

@@ -116,14 +116,11 @@ int dasd_scan_partitions(struct dasd_block *block)
 			      rc);
 		return -ENODEV;
 	}
-	/*
-	 * See fs/partition/check.c:register_disk,rescan_partitions
-	 * Can't call rescan_partitions directly. Use ioctl.
-	 */
-	rc = ioctl_by_bdev(bdev, BLKRRPART, 0);
+
+	rc = blkdev_reread_part(bdev);
 	while (rc == -EBUSY && retry > 0) {
 		schedule();
-		rc = ioctl_by_bdev(bdev, BLKRRPART, 0);
+		rc = blkdev_reread_part(bdev);
 		retry--;
 		DBF_DEV_EVENT(DBF_ERR, block->base,
 			      "scan partitions error, retry %d rc %d",