Camera3: Remove mutex from ZoomRatioMapper

ZoomRatioMapper's member variables are const after construction. As a
result, we don't need mutex to protect updateCaptureRequest and
updateCaptureResult calls.

Also fixed missing zoom ratio mapping initialization for physical
sub-camera.

Test: testZoomRatio CTS
Bug: 130025314
Change-Id: Ibe2ff7cffb13178dcf70fc9e2eb044184e58bcf2