net: mvpp2: allocate zeroed tx descriptors

Reserved and unused fields in the Tx descriptors should be 0. The PPv2
driver doesn't clear them at run-time (for performance reasons) but
these descriptors aren't zeroed when allocated, which can lead to
unpredictable behaviors. This patch fixes this by using
dma_zalloc_coherent instead of dma_alloc_coherent.

Fixes: 3f518509 ("ethernet: Add new driver for Marvell Armada 375 network unit")
Signed-off-by: NYan Markman <ymarkman@marvell.com>
[Antoine: commit message]
Signed-off-by: NAntoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvpp2.c

@@ -5598,7 +5598,7 @@ static int mvpp2_aggr_txq_init(struct platform_device *pdev,
 	u32 txq_dma;
 
 	/* Allocate memory for TX descriptors */
-	aggr_txq->descs = dma_alloc_coherent(&pdev->dev,
+	aggr_txq->descs = dma_zalloc_coherent(&pdev->dev,
 				MVPP2_AGGR_TXQ_SIZE * MVPP2_DESC_ALIGNED_SIZE,
 				&aggr_txq->descs_dma, GFP_KERNEL);
 	if (!aggr_txq->descs)