igb/igbvf: cleanup exception handling in tx_map_adv

After removing the skb_dma_map/unmap calls the exception handling in
igb_tx_map_adv is not correct.  The issue is that the count value was not
being correctly handled so as a result we were not rewinding the ring as
back as we should have been.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/igb/igb_main.c b/drivers/net/igb/igb_main.c
index 933c64f..2ca1734 100644
--- a/drivers/net/igb/igb_main.c
+++ b/drivers/net/igb/igb_main.c
@@ -3584,6 +3584,7 @@
 	for (f = 0; f < skb_shinfo(skb)->nr_frags; f++) {
 		struct skb_frag_struct *frag;
 
+		count++;
 		i++;
 		if (i == tx_ring->count)
 			i = 0;
@@ -3605,7 +3606,6 @@
 		if (pci_dma_mapping_error(pdev, buffer_info->dma))
 			goto dma_error;
 
-		count++;
 	}
 
 	tx_ring->buffer_info[i].skb = skb;