Camera: Clarify AF_REGIONS behavior in capture_result

If application specifies 0-weight AF_REGIONS in capture request, the
camera device is allowed to override with non-0-weight AF_REGIONS in
capture result.

Test: Build
Bug: 29398609
Change-Id: I1e90c6c1717a894458b9a989cbd25981eaad43fb
1 file changed