virtio: fix virtio_config_ops description

- get_features has returned 64 bits since commit d0254773
  ("virtio: add support for 64 bit features.")
- properly mark all optional callbacks
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

include/linux/virtio_config.h

@@ -22,7 +22,7 @@ struct irq_affinity;
  *	offset: the offset of the configuration field
  *	buf: the buffer to read the field value from.
  *	len: the length of the buffer
- * @generation: config generation counter
+ * @generation: config generation counter (optional)
  *	vdev: the virtio_device
  *	Returns the config generation counter
  * @get_status: read the status byte
@@ -48,17 +48,17 @@ struct irq_affinity;
  * @del_vqs: free virtqueues found by find_vqs().
  * @get_features: get the array of feature bits for this device.
  *	vdev: the virtio_device
- *	Returns the first 32 feature bits (all we currently need).
+ *	Returns the first 64 feature bits (all we currently need).
  * @finalize_features: confirm what device features we'll be using.
  *	vdev: the virtio_device
  *	This gives the final feature bits for the device: it can change
  *	the dev->feature bits if it wants.
  *	Returns 0 on success or error status
- * @bus_name: return the bus name associated with the device
+ * @bus_name: return the bus name associated with the device (optional)
  *	vdev: the virtio_device
  *      This returns a pointer to the bus name a la pci_name from which
  *      the caller can then copy.
- * @set_vq_affinity: set the affinity for a virtqueue.
+ * @set_vq_affinity: set the affinity for a virtqueue (optional).
  * @get_vq_affinity: get the affinity for a virtqueue (optional).
  */
 typedef void vq_callback_t(struct virtqueue *);