net: dsa: microchip: Make ksz8_w_sta_mac_table() static

Since ksz8_w_sta_mac_table() is only used within ksz8795.c, make it static
to limit its scope.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>