net: mscc: ocelot: remove the "new" variable in ocelot_port_mdb_add

It is Not Needed, a comment will suffice.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>