net: ethernet: support of_get_mac_address new ERR_PTR error

There was NVMEM support added to of_get_mac_address, so it could now
return ERR_PTR encoded error values, so we need to adjust all current
users of of_get_mac_address to this new fact.

While at it, remove superfluous is_valid_ether_addr as the MAC address
returned from of_get_mac_address is always valid and checked by
is_valid_ether_addr anyway.

Fixes: d01f449c00 ("of_net: add NVMEM support to of_get_mac_address")
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aeroflex/greth.c

@@ -1459,7 +1459,7 @@ static int greth_of_probe(struct platform_device *ofdev)
 		const u8 *addr;
 
 		addr = of_get_mac_address(ofdev->dev.of_node);
-		if (addr) {
+		if (!IS_ERR(addr)) {
 			for (i = 0; i < 6; i++)
 				macaddr[i] = (unsigned int) addr[i];
 		} else {