usb: dwc3: gadget: Resume pending requests after CLEAR_STALL

The function driver may queue new requests right after halting the
endpoint (i.e. queue new requests while the endpoint is stalled).
There's no restriction preventing it from doing so. However, dwc3
currently drops those requests after CLEAR_STALL. The driver should only
drop started requests. Keep the pending requests in the pending list to
resume and process them after the host issues ClearFeature(Halt) to the
endpoint.

Cc: stable@vger.kernel.org
Fixes: cb11ea56 ("usb: dwc3: gadget: Properly handle ClearFeature(halt)")
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>