usb: dwc3: gadget: remove unused 'first_trb_index'

Recent changes have turned this field obsolete. Remove it.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/core.h

@@ -705,7 +705,6 @@ struct dwc3_hwparams {
  * @dep: struct dwc3_ep owning this request
  * @sg: pointer to first incomplete sg
  * @num_pending_sgs: counter to pending sgs
- * @first_trb_index: index to first trb used by this request
  * @epnum: endpoint number to which this request refers
  * @trb: pointer to struct dwc3_trb
  * @trb_dma: DMA address of @trb
@@ -720,7 +719,6 @@ struct dwc3_request {
 	struct scatterlist	*sg;
 
 	unsigned		num_pending_sgs;
-	u8			first_trb_index;
 	u8			epnum;
 	struct dwc3_trb		*trb;
 	dma_addr_t		trb_dma;

drivers/usb/dwc3/gadget.c

@@ -832,7 +832,6 @@ static void dwc3_prepare_one_trb(struct dwc3_ep *dep,
 		dwc3_gadget_move_started_request(req);
 		req->trb = trb;
 		req->trb_dma = dwc3_trb_dma_offset(dep, trb);
-		req->first_trb_index = dep->trb_enqueue;
 		dep->queued_requests++;
 	}