net: dsa: microchip: ksz8: ksz8_fdb_dump: avoid extracting ghost entry from empty...

net: dsa: microchip: ksz8: ksz8_fdb_dump: avoid extracting ghost entry from empty dynamic MAC table.

If the dynamic MAC table is empty, we will still extract one outdated
entry. Fix it by using correct bit offset.

Fixes: 4b20a07e103f ("net: dsa: microchip: ksz8795: add support for ksz88xx chips")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>