usb: dwc3: gadget: Account for link TRB in TRBs left

The TRBs left calculation didn't account for the link TRB taking up one
spot.

If the trb_dequeue < trb_enqueue, then the result includes the link
TRB slot so it must be adjusted.
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -868,6 +868,9 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep)
 	trbs_left = dep->trb_dequeue - dep->trb_enqueue;
 	trbs_left %= DWC3_TRB_NUM;
 
+	if (dep->trb_dequeue < dep->trb_enqueue)
+		trbs_left--;
+
 	return trbs_left;
 }