Fix for UnmapPartitionOnDeviceMapper am: 94fa3e525f am: 447aa85934

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3380291

Change-Id: Ic0288b194959a35bb4e59dedf66d611e19af30f5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>