USB generic driver
Clemens Ladisch <clemens@ladisch.de>
deactivate_urbs didn't return the number of still-active URBs when not
unlinking asynchronously, which would prevent calling wait_clear_urbs
when some URBs actually are being unlinked asynchronously, so these
URBs would be freed while still in use.

I removed deactivate_urb's return value because wait_clear_urbs does
its own counting anyway.