usb: dwc3: ep0: return early on NULL requests

if our list of requests is empty, return early.

There's really nothing to be done in case our
request list is empty anyway because the only
situation where we our list is empty, is when
we're transferring ZLPs.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/ep0.c

@@ -789,9 +789,6 @@ static void dwc3_ep0_complete_data(struct dwc3 *dwc,
 
 	dwc->ep0_next_event = DWC3_EP0_NRDY_STATUS;
 
-	r = next_request(&ep0->request_list);
-	ur = &r->request;
-
 	trb = dwc->ep0_trb;
 
 	status = DWC3_TRB_SIZE_TRBSTS(trb->size);
@@ -804,6 +801,12 @@ static void dwc3_ep0_complete_data(struct dwc3 *dwc,
 		return;
 	}
 
+	r = next_request(&ep0->request_list);
+	if (!r)
+		return;
+
+	ur = &r->request;
+
 	length = trb->size & DWC3_TRB_SIZE_MASK;
 
 	if (dwc->ep0_bounced) {