vdpa/mlx5: Update Control VQ callback information

The control VQ specific information is stored in the dedicated struct
mlx5_control_vq. When the callback is updated through
mlx5_vdpa_set_vq_cb(), make sure to update the control VQ struct.

Fixes: 5262912e ("vdpa/mlx5: Add support for control VQ and MAC setting")
Signed-off-by: Eli Cohen <elic@nvidia.com>
Message-Id: <20220613075958.511064-1-elic@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com)>