usb: dwc3: gadget: make to increment req->remaining in all cases

Sometimes, we might get a completion for a TRB which is left with HWO
bit. Even in these cases, we should increment req->remaining to
properly report total transferred size. I noticed this while debuggin
a separate problem seen with MSC tests from USBCV. Sometimes we would
erroneously report a completion for a 512-byte transfer when, in
reality, we transferred 0 bytes.

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