mlxsw: spectrum: Unmap 802.1Q FID before destroying it

Before destroying the 802.1Q FID we should first remove the VID-to-FID
mapping. This makes mlxsw_sp_fid_destroy() symmetric with regards to
mlxsw_sp_fid_create().

Fixes: 14d39461 ("mlxsw: spectrum: Use per-FID struct for the VLAN-aware bridge")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>