net: mediatek: fix checking for NULL instead of IS_ERR() in .probe

devm_ioremap_resource() returns ERR_PTR() value on error, it never
returns NULL, fix it and propagate the returned error upwards.

Fixes: 656e7052 ("net-next: mediatek: add support for MT7623 ethernet")
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Acked-by: John Crispin <blogic@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -1690,8 +1690,8 @@ static int mtk_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	eth->base = devm_ioremap_resource(&pdev->dev, res);
-	if (!eth->base)
-		return -EADDRNOTAVAIL;
+	if (IS_ERR(eth->base))
+		return PTR_ERR(eth->base);
 
 	spin_lock_init(&eth->page_lock);