USB: kill URBs permanently

looking at usb_kill_urb() it seems to me that it is unnecessarily lenient.
In the use case of disconnect() you never want to use the URB again
(for the same device) But leaving urb->reject elevated will make it easier
to avoid races between read/write and disconnect.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>