xor_writer: use 64bit for partition size am: 80e4391ccc

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3349246

Change-Id: I2903df00ff2353309171a99ad95e061b02593f22
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>