virtio: console: Reference counting portdev structs is not needed

Explain in a comment why there's no need to reference-count the portdev
struct: when a device is yanked out, we can't do anything more with it
anyway so just give up doing anything more with the data or the vqs and
exit cleanly.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -1738,6 +1738,14 @@ static void virtcons_remove(struct virtio_device *vdev)
 
 	unregister_chrdev(portdev->chr_major, "virtio-portsdev");
 
+	/*
+	 * When yanking out a device, we immediately lose the
+	 * (device-side) queues.  So there's no point in keeping the
+	 * guest side around till we drop our final reference.  This
+	 * also means that any ports which are in an open state will
+	 * have to just stop using the port, as the vqs are going
+	 * away.
+	 */
 	if (use_multiport(portdev)) {
 		struct port_buffer *buf;
 		unsigned int len;