vdpa: skip suspend/resume ops if not DRIVER_OK

If a vdpa device is not in state DRIVER_OK, then there is no driver state
to preserve, so no need to call the suspend and resume driver ops.

Suggested-by: Eugenio Perez Martin <eperezma@redhat.com&gt;">
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Message-Id: <1707834358-165470-1-git-send-email-steven.sistare@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>