usb: musb: gadget: clear gadget_driver when gadget is stopped

Some musb glue drivers use gadget_driver pointer to know if any gadget
drivers are loaded at some moment and base further decisions on it,
like to do runtime suspend/resume or not. Right now the pointer is
left alone on stop and OMAP musb glue later does wrong runtime_pm
decisions because of it.

Clear the gadget_driver pointer on remove, it's invalid after stop
anyway.
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_gadget.c

@@ -1934,6 +1934,7 @@ static int musb_gadget_stop(struct usb_gadget *g,
 	dev_dbg(musb->controller, "unregistering driver %s\n", driver->function);
 
 	musb->is_active = 0;
+	musb->gadget_driver = NULL;
 	musb_platform_try_idle(musb, 0);
 	spin_unlock_irqrestore(&musb->lock, flags);