net: mvneta: Fix missing DMA region unmap

The Tx descriptor release code currently calls dma_unmap_single() and
dev_kfree_skb_any() if the descriptor is associated with a non-NULL skb.
This is true only for the last fragment of the packet.

This is wrong, however, since every descriptor buffer is DMA mapped and needs
to be unmapped.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -1291,11 +1291,10 @@ static void mvneta_txq_bufs_free(struct mvneta_port *pp,
 
 		mvneta_txq_inc_get(txq);
 
-		if (!skb)
-			continue;
-
 		dma_unmap_single(pp->dev->dev.parent, tx_desc->buf_phys_addr,
 				 tx_desc->data_size, DMA_TO_DEVICE);
+		if (!skb)
+			continue;
 		dev_kfree_skb_any(skb);
 	}
 }