staging: mt7621-eth: fix return value check in mt7621_gsw_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().

Fixes: f079b640 ("staging: mt7621-eth: add gigabit switch driver (GSW)")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-eth/gsw_mt7621.c

@@ -263,8 +263,8 @@ static int mt7621_gsw_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	gsw->base = devm_ioremap_resource(&pdev->dev, res);
-	if (!gsw->base)
-		return -EADDRNOTAVAIL;
+	if (IS_ERR(gsw->base))
+		return PTR_ERR(gsw->base);
 
 	gsw->dev = &pdev->dev;
 	gsw->irq = irq_of_parse_and_map(pdev->dev.of_node, 0);