net: dsa: microchip: ksz9477: remove unused "on" variable

This variable is not used on ksz9477 side. Remove it.

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>