via-velocity: Correct 64-byte alignment for rx buffers

(From the VIA driver). The current code does not guarantee 64-byte
alignment since it simply does

        int add = skb->data & 63;

        skb->data += add;

(via skb_reserve). So for example, if the skb->data address would be
0x10, this would result in 32-byte alignment (0x10 + 0x10).

Correct by adding

        64 - (skb->data & 63)

instead.
Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/via-velocity.c

@@ -1470,7 +1470,8 @@ static int velocity_alloc_rx_buf(struct velocity_info *vptr, int idx)
 	 *	Do the gymnastics to get the buffer head for data at
 	 *	64byte alignment.
 	 */
-	skb_reserve(rd_info->skb, (unsigned long) rd_info->skb->data & 63);
+	skb_reserve(rd_info->skb,
+			64 - ((unsigned long) rd_info->skb->data & 63));
 	rd_info->skb_dma = pci_map_single(vptr->pdev, rd_info->skb->data,
 					vptr->rx.buf_sz, PCI_DMA_FROMDEVICE);