fec_mxc: set ethaddr if fuses burned and not previously set

Without this change, the following message is generated:
	Warning: FEC using MAC address from net device

See doc/README.enetaddr for details.

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>

drivers/net/fec_mxc.c

@@ -980,6 +980,8 @@ static int fec_probe(bd_t *bd, int dev_id, uint32_t base_addr,
 	if (fec_get_hwaddr(edev, dev_id, ethaddr) == 0) {
 		debug("got MAC%d address from fuse: %pM\n", dev_id, ethaddr);
 		memcpy(edev->enetaddr, ethaddr, 6);
+		if (!getenv("ethaddr"))
+			eth_setenv_enetaddr("ethaddr", ethaddr);
 	}
 	return ret;
 err3: