Camera: Clarify SCALER_CROP_REGION usage am: d341edc3e7 am: 1a47fb441a am: 0ed134d9e3

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/12586223

Change-Id: I3125abc8939fffb95697a78998d58c377cece209