USB: visor: always disable uart on close

Always try to disable the uart on close.

Since the switch to tty ports, close will be called as part of shutdown
before disconnect returns. Hence there is no need to check the
disconnected flag, and we can put devices in disabled states also on
driver unbind.

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