vhost: use wfd on functions setting vring call fd

When ioeventfd is emulated using qemu_pipe(), only EventNotifier's wfd
can be used for writing.

Use the recently introduced event_notifier_get_wfd() function to
obtain the fd that our peer must use to signal the vring.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220304100854.14829-3-slp@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost.c

@@ -1287,7 +1287,7 @@ static int vhost_virtqueue_init(struct vhost_dev *dev,
         return r;
     }
 
-    file.fd = event_notifier_get_fd(&vq->masked_notifier);
+    file.fd = event_notifier_get_wfd(&vq->masked_notifier);
     r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
     if (r) {
         VHOST_OPS_DEBUG(r, "vhost_set_vring_call failed");
@@ -1542,9 +1542,9 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
 
     if (mask) {
         assert(vdev->use_guest_notifier_mask);
-        file.fd = event_notifier_get_fd(&hdev->vqs[index].masked_notifier);
+        file.fd = event_notifier_get_wfd(&hdev->vqs[index].masked_notifier);
     } else {
-        file.fd = event_notifier_get_fd(virtio_queue_get_guest_notifier(vvq));
+        file.fd = event_notifier_get_wfd(virtio_queue_get_guest_notifier(vvq));
     }
 
     file.index = hdev->vhost_ops->vhost_get_vq_index(hdev, n);