usb: dwc3: gadget: Reclaim extra TRBs after request completion

An SG request may be partially completed (due to no available TRBs).
Don't reclaim extra TRBs and clear the needs_extra_trb flag until the
request is fully completed. Otherwise, the driver will reclaim the wrong
TRB.

Cc: stable@vger.kernel.org
Fixes: 1f512119 ("usb: dwc3: gadget: add remaining sg entries to ring")
Signed-off-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>