VMS: fix library compatibility settings in util/mkdef.pl

The regexp to parse the incoming version number was flawed, and since
we allow ourselves to add missing APIs in PATCH releases, the
compatibility settings still need to include the PATCH part of the
version number.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7858)