dns/powerdns: fix build on 14.0-CURRENT (+ OpenSSL 3.0.9)

This fixes the way OpenSSL is detected (it now uses a non-deprecated function),
which is not available anymore on 14.0-CURRENT. Doesn't change anything for
previous versions of FreeBSD.

PR:		272231
Reported by:	tremere@cainites.net (maintainer)