rpi: set ethaddr as well

Let's set "ethaddr" when we get the ethernet address too, so that
fdt_fixup_ethernet() sets the address in the device tree and the Linux
driver can pick it up.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>

board/raspberrypi/rpi/rpi.c

@@ -259,6 +259,9 @@ static void set_usbethaddr(void)
 
 	eth_setenv_enetaddr("usbethaddr", msg->get_mac_address.body.resp.mac);
 
+	if (!getenv("ethaddr"))
+		setenv("ethaddr", getenv("usbethaddr"));
+
 	return;
 }