net: ethernet: cpsw: fix erroneous condition in error check

The error check in cpsw_probe_dt() has an '&&' where an '||' is
meant to be. This causes a NULL pointer dereference when incomplet DT
data is passed to the driver ('phy_id' property for cpsw_emac1
missing).

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: David S. Miller <davem@davemloft.net>