Only trees which are in use should be compared to requested prefix usage.
Fixes: 53342023ee ("mlxsw: spectrum_router: Implement LPM trees management")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>