pci: mvebu: fix return value check in mvebu_pcie_probe()

In case of error, function of_clk_get_by_name() returns
ERR_PTR() never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

drivers/pci/host/pci-mvebu.c

@@ -828,7 +828,7 @@ static int __init mvebu_pcie_probe(struct platform_device *pdev)
 		}
 
 		port->clk = of_clk_get_by_name(child, NULL);
-		if (!port->clk) {
+		if (IS_ERR(port->clk)) {
 			dev_err(&pdev->dev, "PCIe%d.%d: cannot get clock\n",
 			       port->port, port->lane);
 			iounmap(port->base);