Fix HDR blownout issue in the Photos app with HDR display on.

- make sure that renderHdrSdrRatio is not larger than current
  mDesiredHdrSdrRatio when updating.
- cleanup setTargetHdrSdrRatio function.

Bug: 276744890
Test: play with Photos
Change-Id: I7fcd5e33633483ff7577d11748874472ad3ca15e