While cpsw is probe dt, it accepts only slaves nodes with "phy_id" property.
In case of fixed-link there are no "phy_id" property and probe would be failed.
This patch avoid the failure due to missing "phy_id" in case of fixed-link.

Signed-off-by: Andreas Schmidt <mail@schmidt-andreas.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>