rpmsg: virtio: Fix the unregistration of the device rpmsg_ctrl

Unregister the rpmsg_ctrl device instead of just freeing the
the virtio_rpmsg_channel structure.
This will properly unregister the device and call
virtio_rpmsg_release_device() that frees the structure.

Fixes: c486682a ("rpmsg: virtio: Register the rpmsg_char device")
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Reviewed-by: Hangyu Hua <hbh25y@gmail.com>
Link: https://lore.kernel.org/r/20220426060536.15594-4-hbh25y@gmail.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

drivers/rpmsg/virtio_rpmsg_bus.c

@@ -862,7 +862,7 @@ static void rpmsg_virtio_del_ctrl_dev(struct rpmsg_device *rpdev_ctrl)
 {
 	if (!rpdev_ctrl)
 		return;
-	kfree(to_virtio_rpmsg_channel(rpdev_ctrl));
+	device_unregister(&rpdev_ctrl->dev);
 }
 
 static int rpmsg_probe(struct virtio_device *vdev)