net: macb: Add null check for PCLK and HCLK

Both PCLK and HCLK are "required" clocks according to macb devicetree
documentation. There is a chance that devm_clk_get doesn't return a
negative error but just a NULL clock structure instead. In such a case
the driver proceeds as usual and uses pclk value 0 to calculate MDC
divisor which is incorrect. Hence fix the same in clock initialization.
Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -3370,14 +3370,20 @@ static int macb_clk_init(struct platform_device *pdev, struct clk **pclk,
 		*hclk = devm_clk_get(&pdev->dev, "hclk");
 	}
 
-	if (IS_ERR(*pclk)) {
+	if (IS_ERR_OR_NULL(*pclk)) {
 		err = PTR_ERR(*pclk);
+		if (!err)
+			err = -ENODEV;
+
 		dev_err(&pdev->dev, "failed to get macb_clk (%u)\n", err);
 		return err;
 	}
 
-	if (IS_ERR(*hclk)) {
+	if (IS_ERR_OR_NULL(*hclk)) {
 		err = PTR_ERR(*hclk);
+		if (!err)
+			err = -ENODEV;
+
 		dev_err(&pdev->dev, "failed to get hclk (%u)\n", err);
 		return err;
 	}