libhealthloop: Micro-optimize HealthLoop::RegisterEvent() am: 6fe3618e7c

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3207757

Change-Id: Ibe11ad3a24504ffbfa9c744df0474606762d411f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>