USB: sierra close race

the sierra driver does not directly use usb_kill_urb(). It uses a wrapper.
This wrapper means that callbacks which are running are not killed during
close, resubmitting and illicitly pushing data into the tty layer.
The whole purpose of usb_kill_urb() is subverted. The wrapper must be removed.
The same problem as the option driver.

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