net: wireless: 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.

Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wireless/ralink/rt2x00/rt2x00dev.c

@@ -1007,7 +1007,7 @@ void rt2x00lib_set_mac_address(struct rt2x00_dev *rt2x00dev, u8 *eeprom_mac_addr
 	const char *mac_addr;
 
 	mac_addr = of_get_mac_address(rt2x00dev->dev->of_node);
-	if (mac_addr)
+	if (!IS_ERR(mac_addr))
 		ether_addr_copy(eeprom_mac_addr, mac_addr);
 
 	if (!is_valid_ether_addr(eeprom_mac_addr)) {