net/nxp/lpc_eth: Drop ifdef CONFIG_OF_NET

Since of_get_mac_address() is now declared even if CONFIG_OF_NET
is not configured, the ifdef is no longer necessary and can be
removed.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>