net: dsa: microchip: ksz8: Make ksz8_r_sta_mac_table() static

As ksz8_r_sta_mac_table() is only used within ksz8795.c, there is no need
to export it. Make the function static for better encapsulation.

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