net: dsa: microchip: ksz8795: use port_cnt instead of TOTOAL_PORT_NUM

To get the driver working with other chips using different port counts
the dyn_mac_table should be flushed depending on the amount of available
ports. This patch remove the extra define TOTOAL_PORT_NUM and is
making use of the dynamic port_cnt variable instead.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>