net: stmmac: remove dead code in stmmac_tx_clean

Since commit cf32deec ("stmmac: add tx_skbuff_dma to save descriptors used by PTP"),
the struct dma_desc *p in stmmac_tx_clean was not used at all.

This patch remove this dead code.
Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
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

@@ -1109,13 +1109,6 @@ static void dma_free_tx_skbufs(struct stmmac_priv *priv)
 	int i;
 
 	for (i = 0; i < DMA_TX_SIZE; i++) {
-		struct dma_desc *p;
-
-		if (priv->extend_desc)
-			p = &((priv->dma_etx + i)->basic);
-		else
-			p = priv->dma_tx + i;
-
 		if (priv->tx_skbuff_dma[i].buf) {
 			if (priv->tx_skbuff_dma[i].map_as_page)
 				dma_unmap_page(priv->device,