usb: chipidea: udc: don't assign gadget.dev.release directly

udc-core provides a better way to handle release
methods, let's use it.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/chipidea/udc.c

@@ -1688,16 +1688,6 @@ static irqreturn_t udc_irq(struct ci13xxx *ci)
 	return retval;
 }
 
-/**
- * udc_release: driver release function
- * @dev: device
- *
- * Currently does nothing
- */
-static void udc_release(struct device *dev)
-{
-}
-
 /**
  * udc_start: initialize gadget role
  * @ci: chipidea controller
@@ -1717,8 +1707,6 @@ static int udc_start(struct ci13xxx *ci)
 
 	INIT_LIST_HEAD(&ci->gadget.ep_list);
 
-	ci->gadget.dev.release  = udc_release;
-
 	/* alloc resources */
 	ci->qh_pool = dma_pool_create("ci13xxx_qh", dev,
 				       sizeof(struct ci13xxx_qh),