ssh: correct parse_cert_times case for hex "to" time

This appeared to be a copy-paste error from the "from" time case above.

Reported by: Coverity Scan
CID: 1500407
Reviewed by: markj
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D37252

(cherry picked from commit 0657b2325df3d85967870a928d58b24ffcf3f1ea)