IB/mlx5: Set mlx5_query_roce_port's return value to void

In case of an error, the properties reported to user
are zeroed out, so no need for a return value.

Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>