net: ethernet: bgmac: Fix return value check in bgmac_probe()

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: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bgmac-platform.c

@@ -141,7 +141,7 @@ static int bgmac_probe(struct platform_device *pdev)
 	}
 
 	bgmac->plat.idm_base = devm_ioremap_resource(&pdev->dev, regs);
-	if (!bgmac->plat.idm_base) {
+	if (IS_ERR(bgmac->plat.idm_base)) {
 		dev_err(&pdev->dev, "Unable to map idm resource\n");
 		return PTR_ERR(bgmac->plat.idm_base);
 	}