usb: dwc3: gadget: assign resource_index inside get_transfer_index()

Instead of returning resource index number just to assign it to a
field inside 'dep' which was passed as argument, we can assing
dep->resource_index from inside dwc3_gadget_ep_get_transfer_index()
itself.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/ep0.c

@@ -79,7 +79,7 @@ static int dwc3_ep0_start_trans(struct dwc3_ep *dep)
 	if (ret < 0)
 		return ret;
 
-	dep->resource_index = dwc3_gadget_ep_get_transfer_index(dep);
+	dwc3_gadget_ep_get_transfer_index(dep);
 	dwc->ep0_next_event = DWC3_EP0_COMPLETE;
 
 	return 0;