Mark source partition as writable before writing corrected bits am: cf29915f47 am: 8f19b57ef0

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2626759

Change-Id: I4a54a5bdde4d24dde2aa9677dadac06a5e34a66a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>