SF TimeStats: fix a hazard issue

The setAcquireFence and setDesiredTime could happen in between the
splited setLayerName and setPostTime, where setLayerName inserts an
entry but setPostTime actually initializes the structure and waitData
position. This change combine setLayerName and setPostTime again to
eliminate the hazard.

Test: build
Bug: b/118770127
Change-Id: Ia1961cb688bbabf23d88305750e69c9fa41da8dd