postsummary_revId should be topicsummary_revId

Click on the timestamp in a topic summary under topic history, get exception.

Bug: 64385
Change-Id: I8d975f0ce0eadae24e0691a11e3d3a5e592b7cfc
(cherry picked from commit 499ed477a989916d20a5fac559d99b1e35011098)