usb: dwc3: warn on once when no trbs

Seems last time we hit few issues where
we get trb_left = 0, mainly because of
HWO bit still set in previous TRB.
Add warn on once to catch/fix such
problems much faster.
Signed-off-by: Janusz Dziedzic <januszx.dziedzic@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -937,6 +937,7 @@ static struct dwc3_trb *dwc3_ep_prev_trb(struct dwc3_ep *dep, u8 index)
 static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep)
 {
 	struct dwc3_trb		*tmp;
+	struct dwc3		*dwc = dep->dwc;
 	u8			trbs_left;
 
 	/*
@@ -948,7 +949,8 @@ static u32 dwc3_calc_trbs_left(struct dwc3_ep *dep)
 	 */
 	if (dep->trb_enqueue == dep->trb_dequeue) {
 		tmp = dwc3_ep_prev_trb(dep, dep->trb_enqueue);
-		if (tmp->ctrl & DWC3_TRB_CTRL_HWO)
+		if (dev_WARN_ONCE(dwc->dev, tmp->ctrl & DWC3_TRB_CTRL_HWO,
+				  "%s No TRBS left\n", dep->name))
 			return 0;
 
 		return DWC3_TRB_NUM - 1;