MFH: r409954: security/py-cryptography: Fix build with OpenSSL 1.0.2g

Backport upstream commit [1] fixing build failures after the OpenSSL
1.0.2g update

[1] https://github.com/pyca/cryptography/commit/df779dfec9ce87b79e48448aea3c597a4716b29e

PR: 207624
Reported by: matthew, Pierre Guinoiseau <pierre guinoiseau eu>

Approved by: ports-secteam (blanket)