Fix static checker warnings in the flow of system guid query.

Fixes: 707c4602 ('net/mlx5_core: Add new query HCA vport commands')
Signed-off-by: NMajd Dibbiny <majd@mellanox.com>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>