Fix `xsprintf` callback
Fix `xsprintf` callback

Summary: After all that, I forgot to change this back.

Test Plan: Eyeball it.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11735

aik099/arcanist,wxstars/arcanist,alexmv/arcanist,KieranHayes/arcanist,wikimedia/phabricator-arcanist,codelabs-ch/arcanist,r4nt/arcanist,wxstars/arcanist,calblueprint/arcanist,calblueprint/arcanist,coursera/arcanist,alexmv/arcanist,wxstars/arcanist,hach-que/arcanist,uber/arcanist,hach-que/arcanist,jra3/arcanist,calblueprint/arcanist,phacility/arcanist,chundongwang/arcanist,uber/arcanist,alexmv/arcanist,fivestars/arcanist,eSpark/arcanist,fivestars/arcanist,memsql/arcanist,Symplicity/arcanist,KieranHayes/arcanist,codelabs-ch/arcanist,sneakpeeq/arcanist,fivestars/arcanist,wikimedia/phabricator-arcanist,haskell-infra/arcanist,PageUpPeopleOrg/arcanist-patches,sneakpeeq/arcanist,folsom-labs/arcanist,coursera/arcanist,memsql/arcanist,Symplicity/arcanist,sneakpeeq/arcanist,r4nt/arcanist,folsom-labs/arcanist,PageUpPeopleOrg/arcanist-patches,eSpark/arcanist,memsql/arcanist,folsom-labs/arcanist,Khan/arcanist,calblueprint/arcanist,wxstars/arcanist,zhihu/arcanist,wharris/arcanist,wikimedia/phabricator-arcanist,coursera/arcanist,wharris/arcanist,zhihu/arcanist,hach-que/arcanist,aik099/arcanist,aik099/arcanist,r4nt/arcanist,alexmv/arcanist,Khan/arcanist,eSpark/arcanist,wharris/arcanist,PageUpPeopleOrg/arcanist-patches,uber/arcanist,kevinseelbach/arcanist,phacility/arcanist,aik099/arcanist,Symplicity/arcanist,zhihu/arcanist,phacility/arcanist,zhihu/arcanist,haskell-infra/arcanist,wharris/arcanist,eSpark/arcanist,KieranHayes/arcanist,fivestars/arcanist,codelabs-ch/arcanist,folsom-labs/arcanist,kevinseelbach/arcanist,Symplicity/arcanist,KieranHayes/arcanist,Khan/arcanist,codelabs-ch/arcanist,memsql/arcanist,chundongwang/arcanist,phacility/arcanist,jra3/arcanist,jra3/arcanist,haskell-infra/arcanist,haskell-infra/arcanist,chundongwang/arcanist,wikimedia/phabricator-arcanist,jra3/arcanist,kevinseelbach/arcanist,coursera/arcanist,codelabs-ch/arcanist,Khan/arcanist,phacility/arcanist,chundongwang/arcanist,hach-que/arcanist,uber/arcanist,r4nt/arcanist,kevinseelbach/arcanist,PageUpPeopleOrg/arcanist-patches,sneakpeeq/arcanist