net: dsa: sja1105: error out on unsupported PHY mode

The driver continues probing when a port is configured for an
unsupported PHY interface type, instead it should stop.

Fixes: 8aa9ebcc ("net: dsa: Introduce driver for NXP SJA1105 5-port L2 switch")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>