net: stmmac: Prevent divide-by-zero

When RX Coalesce settings are set to all zero (which is a valid setting)
we will currently get a divide-by-zero error. Fix it.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -3418,7 +3418,9 @@ static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
 		stmmac_refill_desc3(priv, rx_q, p);
 
 		rx_q->rx_count_frames++;
-		rx_q->rx_count_frames %= priv->rx_coal_frames;
+		rx_q->rx_count_frames += priv->rx_coal_frames;
+		if (rx_q->rx_count_frames > priv->rx_coal_frames)
+			rx_q->rx_count_frames = 0;
 		use_rx_wd = priv->use_riwt && rx_q->rx_count_frames;
 
 		dma_wmb();