[patch] sysutils/lire: point to DocBook-XML

I build the lire port today, and noticed, that it did not
pick up docbookx.dtd from DocBook-XML correctly, but it was
configured to use DocBook-SGML, and it didn't even find
that .dtd.

With my patch, `lire' is able procduce HTML output, and
also probably PDF output (not tested, but it relies on
DocBook, too).

PR: ports/57229
Submitted by: Simon Barner <barner@in.tum.de>