Camera: Update doc to allow maxDigitalZoom to be less than maxZoomRatio am: c8f279004f am: 1756cb6d8f

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/media/+/12354170

Change-Id: I8b5416df8736cd86be1d31f5b218639537e09f11