Handle the stall condition just like the bable one since in both cases

Handle the stall condition just like the bable one since in both cases
the ring is halted.

Do not bother reporting USBD_STALLED to the stack like other HC drivers
do since the endpoint is automatically reseted.  What is the point of
this error apart from making sure driver authors will forget to call
usbd_clear_endpoint_stall_async() correctly?

The Renesas uPD720202 xHCI, provided by Stefan Wollny, now works as
expected.