net: bgmac: Fix infinite loop in bgmac_dma_tx_add()

Nothing is decrementing the index "i" while we are cleaning up the
fragments we could not successful transmit.

Fixes: 9cde9450 ("bgmac: implement scatter/gather support")
Reported-by: coverity (CID 1352048)
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bgmac.c

@@ -231,7 +231,7 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
 	dma_unmap_single(dma_dev, slot->dma_addr, skb_headlen(skb),
 			 DMA_TO_DEVICE);
 
-	while (i > 0) {
+	while (i-- > 0) {
 		int index = (ring->end + i) % BGMAC_TX_RING_SLOTS;
 		struct bgmac_slot_info *slot = &ring->slots[index];
 		u32 ctl1 = le32_to_cpu(ring->cpu_base[index].ctl1);