reportbuilder: fix javadoc error: no summary or caption for table

Change-Id: I5697ebe0481491d70ee728cac5343aaf892ad29f
Reviewed-on: https://gerrit.libreoffice.org/11242
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>