Changed new_cow_size var type to auto to prevent overflow. am: d4806f80d8 am: bbf031b5ee

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2364279

Change-Id: Ied28d7ea44dfb3a0e983b22a58fa5ee7e5daade3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>