usb: cdnsp: Fix lack of removing request from pending list.

Patch fixes lack of removing request from ep->pending_list on failure
of the stop endpoint command. Driver even after failing this command
must remove request from ep->pending_list.
Without this fix driver can stuck in cdnsp_gadget_ep_disable function
in loop:
        while (!list_empty(&pep->pending_list)) {
                preq = next_request(&pep->pending_list);
                cdnsp_ep_dequeue(pep, preq);
        }

Fixes: 3d829045

 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Link: https://lore.kernel.org/r/20210420042813.34917-1-pawell@gli-login.cadence.com
Signed-off-by: Peter Chen <peter.chen@kernel.org>