USB: quatech2: fix close and disconnect urb handling

Kill urbs unconditionally at close and disconnect.

Note that URB status is not valid outside of completion handler.

Cc: <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>