usb: dwc3: gadget: handle ep_dequeue in LPM properly

Currently, the driver is relying on remove_requests or
ep_dequeue to giveback the requests to function driver,
but when the stop active transfer is called it will
return with error status and will bail out from remove
request without clearing the requests. At this point
we rely on ep_dequeue to clear those requests, but since
usb is disconnected, it will be in LPM which would
drive dequeue to bailout without clearing the requests.

Fix this by removing the LPM check from dequeue to
stop_active_transfer. Now if dequeue process proceeds
will check in stop_active_transfer, if dwc3 is in lpm
bail out from the process. Dequeue will further proceed
& clean up the request from cancelled list.

Change-Id: I13628ab96059fbae14bed64056ff8d7561cd240f
Signed-off-by: Udipto Goswami <ugoswami@codeaurora.org>