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

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

Change-Id: I2c2119157733d99cc56a1cb91fb357b96d63e1c7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>