[services] Blob - fix callback

Summary: This fixes the CI, I mistakenly and prematurely used terminateCallback while I needed to use doneCallback

Test Plan: build services successfully

Reviewers: geekbrother, palys-swm, varun, jimpo

Reviewed By: palys-swm

Subscribers: ashoat, palys-swm, Adrian, atul, benschac, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3607