Camera: Fix off-by-1 error for scaling crop region

Make sure the scaling of coordinates based on zoomRatio is symmetric
relative to the center of the image. And use the center of the pixel
for calculation.

Test: testZoomRatio, testDigitalZoom, cameraservice_test
Test: vendor testing
Bug: 153959755
Change-Id: I966bd31bde5afd50462a018590c7a4fefc3eaac6