net: dsa: sja1105: fix sja1105_parse_rgmii_delays()

This function was using configuration of port 0 in devicetree for all ports.
In case CPU port was not 0, the delay settings was ignored. This resulted not
working communication between CPU and the switch.

Fixes: f5b8631c ("net: dsa: sja1105: Error out if RGMII delays are requested in DT")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>