SoundPool: Set completion flag before promise

Restores order of setting and promise changed by
commit eaeced3383fc398e657b02452952f1a3db6285a1

Test: android.media.cts.SoundPool(Aac|Haptic|Midi|Ogg)Test
Bug: 151161792
Change-Id: I0e9cc173dbcc6080bfbbd15e1cab059812f54c97
1 file changed