usb: dwc3: clean TRB if STARTTRANSFER fail

In case STARTTRANSFER will fail, clean TRB.
Seems HW in such case don't clean HWO bit.
So, without this cleanup prev_trb still have
HWO bit set.

In my case (without patch), after first START failed:
- dep->enqueue == 1
- dep->dequeue == 1
- prev_trb still have HWO set
- left_trb() == 0
No way to send more data.

Signed-off-by: Janusz Dziedzic <januszx.dziedzic@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>