drivers/staging/mt7621-eth: Use dma_zalloc_coherent to replace dma_alloc_coherent+memset

we prefer to use dma_zalloc_coherent rather than dam_alloc_coherent+memset
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-eth/mtk_eth_soc.c

@@ -1396,14 +1396,13 @@ static int mtk_qdma_tx_alloc_tx(struct mtk_eth *eth)
 	if (!ring->tx_buf)
 		goto no_tx_mem;
 
-	ring->tx_dma = dma_alloc_coherent(eth->dev,
+	ring->tx_dma = dma_zalloc_coherent(eth->dev,
 					  ring->tx_ring_size * sz,
 					  &ring->tx_phys,
 					  GFP_ATOMIC | __GFP_ZERO);
 	if (!ring->tx_dma)
 		goto no_tx_mem;
 
-	memset(ring->tx_dma, 0, ring->tx_ring_size * sz);
 	for (i = 0; i < ring->tx_ring_size; i++) {
 		int next = (i + 1) % ring->tx_ring_size;
 		u32 next_ptr = ring->tx_phys + next * sz;