usb: dwc3: gadget: increment dequeue pointer on completion

Instead of waiting until giveback before
incrementing the dequeue pointer, we can increment
it from dwc3_cleanup_done_reqs(), that way we avoid
an extra loop over all TRBs during giveback.

While at that, also avoid using req->first_trb_index
as that's completely unnecessary. A follow-up patch
will clean up further uses of that and remove the
field altogether.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -174,15 +174,8 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
 		int status)
 {
 	struct dwc3			*dwc = dep->dwc;
-	int				i;
 
-	if (req->started) {
-		i = 0;
-		do {
-			dwc3_ep_inc_deq(dep);
-		} while(++i < req->request.num_mapped_sgs);
 	req->started = false;
-	}
 	list_del(&req->list);
 	req->trb = NULL;
 
@@ -2004,7 +1997,6 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 {
 	struct dwc3_request	*req;
 	struct dwc3_trb		*trb;
-	unsigned int		slot;
 	unsigned int		i;
 	int			count = 0;
 	int			ret;
@@ -2019,12 +2011,9 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 		chain = req->request.num_mapped_sgs > 0;
 		i = 0;
 		do {
-			slot = req->first_trb_index + i;
-			if (slot == DWC3_TRB_NUM - 1)
-				slot++;
-			slot %= DWC3_TRB_NUM;
-			trb = &dep->trb_pool[slot];
+			trb = &dep->trb_pool[dep->trb_dequeue];
 			count += trb->size & DWC3_TRB_SIZE_MASK;
+			dwc3_ep_inc_deq(dep);
 
 			ret = __dwc3_cleanup_done_trbs(dwc, dep, req, trb,
 					event, status, chain);