USB: sierra: do not resume I/O on closed ports

Do not resume any I/O, including the delayed write queue, on closed
ports.

Note that this currently has no functional impact due to the
usb_autopm_get_interface() in close(), but that call is about to be
removed by a follow-up patch.

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