usb: gadget: net2280: Fix net2280_dequeue()

When a request must be dequeued with net2280_dequeue() e.g. due
to a device clear action and the same request is finished by the
function scan_dma_completions() then the function net2280_dequeue()
does not find the request in the following search loop and
returns the error -EINVAL without restoring the status ep->stopped.
Thus the endpoint keeps blocked and does not receive any data
anymore.
This fix restores the status and does not issue an error message.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>