Correct use of the paging API in Phame

Summary: Ref T13266. This callsite is using the older API; swap it to use pagers.

Test Plan: Viewed a Phame blog post with siblings, saw the previous/next posts linked.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: nicolast

Maniphest Tasks: T13263, T13266

Differential Revision: https://secure.phabricator.com/D20319