net: fec_ptp: add clock rate zero check

Add clock rate zero check to fix coverity issue of "divide by 0".

Fixes: commit 85bd1798 ("net: fec: fix spin_lock dead lock")
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_ptp.c

@@ -604,6 +604,10 @@ void fec_ptp_init(struct platform_device *pdev, int irq_idx)
 	fep->ptp_caps.enable = fec_ptp_enable;
 
 	fep->cycle_speed = clk_get_rate(fep->clk_ptp);
+	if (!fep->cycle_speed) {
+		fep->cycle_speed = NSEC_PER_SEC;
+		dev_err(&fep->pdev->dev, "clk_ptp clock rate is zero\n");
+	}
 	fep->ptp_inc = NSEC_PER_SEC / fep->cycle_speed;
 
 	spin_lock_init(&fep->tmreg_lock);