gianfar: Fix a bug where the pointer never moves for dma_unmap...

The loop that unmaps all of the TX Buffer Descriptors never actually
moves the txbd pointer, so we were just repeatedly unmapping the first one.
Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/gianfar.c

@@ -635,6 +635,8 @@ static void free_skb_resources(struct gfar_private *priv)
 			dev_kfree_skb_any(priv->tx_skbuff[i]);
 			priv->tx_skbuff[i] = NULL;
 		}
+
+		txbdp++;
 	}
 
 	kfree(priv->tx_skbuff);