net: macb: Pass same size to DMA_UNMAP as used for DMA_MAP

Just as commit "net: macb: DMA-unmap full rx-buffer"
(48330e08), pass the size that
was used for mapping the memory also to the unmap routine to
avoid warnings from the DMA_API.
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb.c

@@ -1113,7 +1113,7 @@ static void gem_free_rx_buffers(struct macb *bp)
 
 		desc = &bp->rx_ring[i];
 		addr = MACB_BF(RX_WADDR, MACB_BFEXT(RX_WADDR, desc->addr));
-		dma_unmap_single(&bp->pdev->dev, addr, skb->len,
+		dma_unmap_single(&bp->pdev->dev, addr, bp->rx_buffer_size,
 				 DMA_FROM_DEVICE);
 		dev_kfree_skb_any(skb);
 		skb = NULL;