vdpa/mlx5: Correct default number of queues when MQ is on

The standard specifies that the initial number of queues is the
default, which is 1 (1 tx, 1 rx).

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230727172354.68243-2-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>