catch mutex when notify sampling rate changed, otherwise signal may be lost am: e1e361ed43 am: ab8e9f1b2b

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

Change-Id: I5a0567009ee8e9c6ae792888ea9992f6d2ea1442
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>