greybus: hd: fix host-device-removal race

Make sure to tear down the svc and flush any on-going hotplug processing
before removing the remaining interfaces.

This fixes crashes due to host-device removal racing with svc
hotplug/unplug processing (e.g. at "UniPro restart").

Testing Done:
Verified that this fixes crashes reproducible on SDB when unloading the
host-device driver module while generating hotplug/unplug events.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/hd.c

@@ -135,9 +135,12 @@ EXPORT_SYMBOL_GPL(gb_hd_add);
 
 void gb_hd_del(struct gb_host_device *hd)
 {
-	gb_interfaces_remove(hd);
-
+	/*
+	 * Tear down the svc and flush any on-going hotplug processing before
+	 * removing the remaining interfaces.
+	 */
 	gb_svc_del(hd->svc);
+	gb_interfaces_remove(hd);
 
 	device_del(&hd->dev);
 }