Remove bogus (and unnecessary) test for serial->dev being NULL in close.

The device is never cleared, and close is never called after a completed
disconnect anyway.

Remove some out-commented bogus code while at it.
Signed-off-by: NJohan Hovold <jhovold@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>