xhci: Don't always run the default stop endpoint command completion handler

The default stop endpoint completion handler will give back cancelled
URBs, and clean, or move past those canceller TRBs on the ring.

This is not always the preferred action.

If the stop endpoint command issuer is waiting for a completion
skip the default handler and just call the completion.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>