usb: dwc3: fix giveback of queued request in ep_dequeue

In case of ep_dequeue , if dequeued request was submitted for dma
transfer, then endpoint is stopped. Once endpoint is stooped, callback
for the dequeued request must be called.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>