fetch: correct env var name for --crl option to work

Reviewed by: grembo
MFC after: 3 days
Security: FreeBSD-SA-24:19.fetch
Approved by: so
Differential Revision: https://reviews.freebsd.org/D46973

(cherry picked from commit 1d7a33888e09f86feb4c2c9f9640d936be07ce9d)
(cherry picked from commit 51676e0a3bd38ab6deae27f72fb6fb6dd648825f)