net: dsa: qca8k: fix broken search_and_del

On deleting an MDB entry for a port, fdb_search_and_del is used.
An FDB entry can't be modified so it needs to be deleted and readded
again with the new portmap (and the port deleted as requested)

We use the SEARCH operator to search the entry to edit by vid and mac
address and then we check the aging if we actually found an entry.

Currently the code suffer from a bug where the searched fdb entry is
never read again with the found values (if found) resulting in the code
always returning -EINVAL as aging was always 0.

Fix this by correctly read the fdb entry after it was searched.

Fixes: ba8f870d

 ("net: dsa: qca8k: add support for mdb_add/del")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>