kernel-doc: better parsing of named variable arguments

Without this patch we get warnings for named variable arguments.

    warning: No description found for parameter '...'
    warning: Excess function parameter 'args' description in 'alloc_ordered_workqueue'

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>