net: stmmac: Fix error handling path in 'alloc_dma_tx_desc_resources()'

If the first 'kmalloc_array' within the loop fails, we should free what
as already been allocated, as done in all other error handling path.

Fixes: ce736788e8a9 ("net: stmmac: adding multiple buffers for TX")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1561,7 +1561,7 @@ static int alloc_dma_tx_desc_resources(struct stmmac_priv *priv)
 						    sizeof(*tx_q->tx_skbuff_dma),
 						    GFP_KERNEL);
 		if (!tx_q->tx_skbuff_dma)
-			return -ENOMEM;
+			goto err_dma_buffers;
 
 		tx_q->tx_skbuff = kmalloc_array(DMA_TX_SIZE,
 						sizeof(struct sk_buff *),