usb: dwc3: gadget: decrement trbs_left for each sg entry

If we don't, we will overwrite valid TRBs.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -924,7 +924,7 @@ static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep,
 			chain = false;
 		}
 
-		if (!trbs_left)
+		if (!trbs_left--)
 			last = true;
 
 		if (last)