usb: dwc3: gadget: use the descriptor pointer we hold

We hold that pointer for one reason. It just
looks nicer to use it.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 4b64dc0..d406a75 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -943,7 +943,7 @@
 		int start_trans;
 
 		start_trans = 1;
-		if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
+		if (usb_endpoint_xfer_isoc(dep->desc) &&
 				dep->flags & DWC3_EP_BUSY)
 			start_trans = 0;