catch mutex when notify sampling rate changed, otherwise signal may be lost am: e1e361ed43

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2496635

Change-Id: I43f3932449efa3dbbc530a8050dc7b4c72328dea
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>