net: stmmac: Fix return value check in qcom_ethqos_probe()

In case of error, the function devm_clk_get() returns ERR_PTR() and
never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().

Fixes: a7c30e62 ("net: stmmac: Add driver for Qualcomm ethqos")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c

@@ -473,8 +473,8 @@ static int qcom_ethqos_probe(struct platform_device *pdev)
 	ethqos->por = of_device_get_match_data(&pdev->dev);
 
 	ethqos->rgmii_clk = devm_clk_get(&pdev->dev, "rgmii");
-	if (!ethqos->rgmii_clk) {
-		ret = -ENOMEM;
+	if (IS_ERR(ethqos->rgmii_clk)) {
+		ret = PTR_ERR(ethqos->rgmii_clk);
 		goto err_mem;
 	}