net: dsa: microchip: ksz8: fix ksz8_fdb_dump()

Before this patch, the ksz8_fdb_dump() function had several issues, such
as uninitialized variables and incorrect usage of source port as a bit
mask. These problems caused inaccurate reporting of vid information and
port assignment in the bridge fdb.

Fixes: e587be75 ("net: dsa: microchip: update fdb add/del/dump in ksz_common")
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>