e100: Release skb when DMA mapping is failed in e100_xmit_prepare

When pci_dma_mapping_error in e100_xmit_prepare is failed, the skb buffer
allocated by netdev_alloc_skb_ip_align in e100_rx_alloc_skb is not
released, which causes a possible resource leak.
This patch adds error handling code to fix it.
Signed-off-by: Jia-Ju Bai <baijiaju1990@163.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e100.c

@@ -1770,8 +1770,11 @@ static int e100_xmit_prepare(struct nic *nic, struct cb *cb,
 	dma_addr = pci_map_single(nic->pdev,
 				  skb->data, skb->len, PCI_DMA_TODEVICE);
 	/* If we can't map the skb, have the upper layer try later */
-	if (pci_dma_mapping_error(nic->pdev, dma_addr))
+	if (pci_dma_mapping_error(nic->pdev, dma_addr)) {
+		dev_kfree_skb_any(skb);
+		skb = NULL;
 		return -ENOMEM;
+	}
 
 	/*
 	 * Use the last 4 bytes of the SKB payload packet as the CRC, used for