usb: gadget: Don't giveback request if ep command times out

Currently driver is giving back requests to gadget even if
the active transfers are not stopped. This might lead the
controller to access the requests which are already unmapped.
This change adds a judgement for giving back the requests to
gadget based on ep command status. Also if ep command times out
and the controller doesn't stop correctly  then mark it as an
error event and restart the USB session.

Change-Id: If32cddddf0544140d5bdf68df9144702e00dc758
Signed-off-by: Udipto Goswami <ugoswami@codeaurora.org>