IB/mlx5: Verify reserved fields are cleared

Verify that reserved fields in struct mlx5_ib_resize_cq are cleared
before continuing execution of the verb. This is required to allow
making use of this area in future revisions.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>