Fix wrongly used enum
Fix wrongly used enum

The function should return cvrf_doc_status_type_t but
CVRF_DOC_PUBLISHER_UNKNOWN is of type cvrf_doc_publisher_type_t.
Fortunately, we have a smilar value CVRF_DOC_STATUS_UNKNOWN
in cvrf_doc_status_type_t which we can use instead.

Addressing:
/home/jcerny/work/git/openscap/src/CVRF/cvrf_enumeration.c: In function ‘cvrf_doc_status_type_parse’:
/home/jcerny/work/git/openscap/src/CVRF/cvrf_enumeration.c:95:9: warning: implicit conversion from ‘enum <anonymous>’ to ‘cvrf_doc_status_type_t’ [-Wenum-conversion]
   95 |  return CVRF_DOC_PUBLISHER_UNKNOWN;
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~

OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap,OpenSCAP/openscap