Camera: Clarify SCALER_CROP_REGION usage am: d341edc3e7 am: 1a47fb441a am: 6c5841ec46

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

Change-Id: I03a7b934e614725d6fcbc9ced52463642e68aa77