net: stmmac: fix return value check in socfpga_dwmac_parse_data()

In case of error, the function devm_ioremap_resource() returns
ERR_PTR() and 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>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c

@@ -120,9 +120,9 @@ static int socfpga_dwmac_parse_data(struct socfpga_dwmac *dwmac, struct device *
 		}
 
 		dwmac->splitter_base = devm_ioremap_resource(dev, &res_splitter);
-		if (!dwmac->splitter_base) {
+		if (IS_ERR(dwmac->splitter_base)) {
 			dev_info(dev, "Failed to mapping emac splitter\n");
-			return -EINVAL;
+			return PTR_ERR(dwmac->splitter_base);
 		}
 	}