virtio_blk: fix type warning

Fix parameter type warning:

linux-next-20081126/drivers/block/virtio_blk.c:307: warning: large integer implicitly truncated to unsigned type
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/block/virtio_blk.c

@@ -304,7 +304,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	if (!err)
 		blk_queue_max_segment_size(vblk->disk->queue, v);
 	else
-		blk_queue_max_segment_size(vblk->disk->queue, -1UL);
+		blk_queue_max_segment_size(vblk->disk->queue, -1U);
 
 	/* Host can optionally specify the block size of the device */
 	err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,