vdpa/mlx5: Set an initial size on the VQ

The virtqueue size is a pre-requisite for setting up any virtqueue
resources. For the upcoming optimization of creating virtqueues at
device add, the virtqueue size has to be configured.

The queue size check in setup_vq() will always be false. So remove it.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Message-Id: <20240626-stage-vdpa-vq-precreate-v2-12-560c491078df@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>