The only place where this variable would be set to false is the
ksz8_config_cpu_port() function. But it is done in a bogus way:

 	for (i = 0; i < dev->phy_port_cnt; i++) {
		if (i == dev->phy_port_cnt) <--- will be never executed.
			break;
		p->on = 1;

So, we never have a situation where p->on = 0. In this case, we can just
remove it.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>