qlcnic: Avoid double free of skb in tx path

buffer->skb should be marked NULL to avoid double free of the skb.

Signed-off-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: Anirban Chakraborty <anirban.chakraborty@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/qlcnic/qlcnic_main.c b/drivers/net/qlcnic/qlcnic_main.c
index 3ab7d2c..0f6af5c 100644
--- a/drivers/net/qlcnic/qlcnic_main.c
+++ b/drivers/net/qlcnic/qlcnic_main.c
@@ -2159,6 +2159,7 @@
 
 	nf = &pbuf->frag_array[0];
 	pci_unmap_single(pdev, nf->dma, skb_headlen(skb), PCI_DMA_TODEVICE);
+	pbuf->skb = NULL;
 }
 
 static inline void