bash completion: Fix help option parsing.

bash completion: Fix help option parsing.

If we complete on para_client or para_audioc options rather than on server
or audiod subcommands, we parse the --help output to determine the options to
complete on. The regular expression we currently use for that is too lenient
because it also matches the options in the synopsis section of the help output.

Fix this by prefixing the expression with '^' to extract only the options
of the subsequent help text.