net: macb: do not copy the mac address if NULL

This patch fixes the MAC address setup in the probe. The MAC address
retrieved using of_get_mac_address was checked for not containing an
error, but it may also be NULL which wasn't tested. Fix it by replacing
IS_ERR with IS_ERR_OR_NULL.

Fixes: 541ddc66 ("net: macb: support of_get_mac_address new ERR_PTR error")
Signed-off-by: NAntoine Tenart <antoine.tenart@bootlin.com>
Acked-by: NNicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/cadence/macb_main.c

@@ -4180,7 +4180,7 @@ static int macb_probe(struct platform_device *pdev)
 	if (PTR_ERR(mac) == -EPROBE_DEFER) {
 		err = -EPROBE_DEFER;
 		goto err_out_free_netdev;
-	} else if (!IS_ERR(mac)) {
+	} else if (!IS_ERR_OR_NULL(mac)) {
 		ether_addr_copy(bp->dev->dev_addr, mac);
 	} else {
 		macb_get_hwaddr(bp);