Fix --lock-video-orientation syntax

The argument for option --lock-video-orientation has been made optional
by 5af9d0ee0faddfca689f468c7d463c86233e8d93.

With getopt_long(), contrary to mandatory arguments, optional arguments
must be given with a '=':

    --lock-video-orientation 2   # wrong, parse error
    --lock-video-orientation=2   # correct