vmbus: unregister device_obj->channels_kset

Without the patch, a device can't be thoroughly destroyed, because
vmbus_device_register() -> kset_create_and_add() still holds a reference
to the hv_device's device.kobj.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Fixes: c2e5df616e1a ("vmbus: add per-channel sysfs info")
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/vmbus_drv.c

@@ -1378,6 +1378,8 @@ void vmbus_device_unregister(struct hv_device *device_obj)
 	pr_debug("child device %s unregistered\n",
 		dev_name(&device_obj->device));
 
+	kset_unregister(device_obj->channels_kset);
+
 	/*
 	 * Kick off the process of unregistering the device.
 	 * This will call vmbus_remove() and eventually vmbus_device_release()