[non-maintainer update] update logic for "BROKEN" variable in audio/aureal-kmod

The current logic to calculate BROKEN in this port does not
allow for one OS release to ask the port if it is broken
on another OS release. This is due to an assumption that
the OSVERSION passed to the Makefile exactly corresponds
to the source version installed under /usr/src/sys (if any.)
That is the default. However, when doing a cross-query,
this is not the case.

While this is a problem that is probably only of interest
to myself, Bill Fenner, and Dan Langille, the logic could
use tightening anyway.

PR: ports/52590
Submitted by: Mark Linimon <linimon@lonesome.com>