usb: hub: keep hub->dev reference all the time when struct usb_hub lives

This is just a small optimization of the fix from the commit c605f3cdff53a743f6
("usb: hub: take hub->hdev reference when processing from eventlist).

We do not need to take the reference for each event. Instead we could get it
when struct usb_hub is allocated and put it when it is released. By other words,
we could handle it the same way as the reference for hub->intfdev.

The motivation is that it will make the life easier when switching from khubd
kthread to a workqueue.

Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hub.c

@@ -1635,6 +1635,7 @@ static void hub_release(struct kref *kref)
 {
 	struct usb_hub *hub = container_of(kref, struct usb_hub, kref);
 
+	usb_put_dev(hub->hdev);
 	usb_put_intf(to_usb_interface(hub->intfdev));
 	kfree(hub);
 }
@@ -1800,6 +1801,7 @@ descriptor_error:
 	INIT_DELAYED_WORK(&hub->leds, led_work);
 	INIT_DELAYED_WORK(&hub->init_work, NULL);
 	usb_get_intf(intf);
+	usb_get_dev(hdev);
 
 	usb_set_intfdata (intf, hub);
 	intf->needs_remote_wakeup = 1;
@@ -5026,10 +5028,9 @@ static void hub_events(void)
 
 		hub = list_entry(tmp, struct usb_hub, event_list);
 		kref_get(&hub->kref);
-		hdev = hub->hdev;
-		usb_get_dev(hdev);
 		spin_unlock_irq(&hub_event_lock);
 
+		hdev = hub->hdev;
 		hub_dev = hub->intfdev;
 		intf = to_usb_interface(hub_dev);
 		dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",
@@ -5142,7 +5143,6 @@ static void hub_events(void)
 		usb_autopm_put_interface(intf);
  loop_disconnected:
 		usb_unlock_device(hdev);
-		usb_put_dev(hdev);
 		kref_put(&hub->kref, hub_release);
 
 	} /* end while (1) */