usb: dwc3: gadget: fixing dequeue of TRBs

A TRB which is dequeued seems to have its HWO bits set to 1. Therefore
we ignore it if we dequeue it after the command is completed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>