virtio: Fix sysfs bits to have proper block symlink

Fix up so that the virtio_blk devices in sysfs link correctly to their
block device.  This then allows them to be detected by hal, etc
Signed-off-by: Jeremy Katz <katzj@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/block/virtio_blk.c

@@ -238,6 +238,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->disk->first_minor = index_to_minor(index);
 	vblk->disk->private_data = vblk;
 	vblk->disk->fops = &virtblk_fops;
+	vblk->disk->driverfs_dev = &vdev->dev;
 	index++;
 
 	/* If barriers are supported, tell block layer that queue is ordered */