usb: dwc3: gadget: dwc3_gadget_del_and_unmap_request() can be static

Fixes the following sparse warning:

drivers/usb/dwc3/gadget.c:169:6: warning:
 symbol 'dwc3_gadget_del_and_unmap_request' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -169,7 +169,7 @@ static void dwc3_ep_inc_deq(struct dwc3_ep *dep)
 	dwc3_ep_inc_trb(&dep->trb_dequeue);
 }
 
-void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep,
+static void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep,
 		struct dwc3_request *req, int status)
 {
 	struct dwc3			*dwc = dep->dwc;