net: dsa: qca8k: fix delay applied to wrong cpu in parse_port_config

Fix delay settings applied to wrong cpu in parse_port_config. The delay
values is set to the wrong index as the cpu_port_index is incremented
too early. Start the cpu_port_index to -1 so the correct value is
applied to address also the case with invalid phy mode and not available
port.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>