Take partition size into account when reporting progress am: 5b14582f19

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2166202

Change-Id: Icb28a400c5941b2f4c3b069f1f73164740c8669e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>