ixgbe: Set IXGBE_RSC_CB(skb)->DMA field to zero after unmapping the address

As per Simon Horman's feedback set IXGBE_RSC_CB(skb)->dma to zero
after unmapping HWRSC DMA address to avoid double freeing.

Signed-off-by:  Mallikarjuna R Chilakala <mallikarjuna.chilakala@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe_main.c

@@ -935,10 +935,12 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
 			if (skb->prev)
 				skb = ixgbe_transform_rsc_queue(skb, &(rx_ring->rsc_count));
 			if (adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) {
-				if (IXGBE_RSC_CB(skb)->dma)
+				if (IXGBE_RSC_CB(skb)->dma) {
 					pci_unmap_single(pdev, IXGBE_RSC_CB(skb)->dma,
 					                 rx_ring->rx_buf_len,
 					                 PCI_DMA_FROMDEVICE);
+					IXGBE_RSC_CB(skb)->dma = 0;
+				}
 				if (rx_ring->flags & IXGBE_RING_RX_PS_ENABLED)
 					rx_ring->rsc_count += skb_shinfo(skb)->nr_frags;
 				else
@@ -3126,10 +3128,12 @@ static void ixgbe_clean_rx_ring(struct ixgbe_adapter *adapter,
 			rx_buffer_info->skb = NULL;
 			do {
 				struct sk_buff *this = skb;
-				if (IXGBE_RSC_CB(this)->dma)
+				if (IXGBE_RSC_CB(this)->dma) {
 					pci_unmap_single(pdev, IXGBE_RSC_CB(this)->dma,
 					                 rx_ring->rx_buf_len,
 					                 PCI_DMA_FROMDEVICE);
+					IXGBE_RSC_CB(this)->dma = 0;
+				}
 				skb = skb->prev;
 				dev_kfree_skb(this);
 			} while (skb);