Fix freeze rate calculations am: 2a3af65ad3

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/23352136

Change-Id: Ic949b37fc8a99fa71b4d1643f42d929d4f9970ee
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>