fix GKI_run return type

Summary: error: void function 'GKI_run' should not return a value [-Wreturn-type]

Test Plan: verify with gcc

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D585

Change-Id: Ib37a121462c9f321d94cdfcf13a763447d350fcd