Fix screenshot motion spec anchor point

Moves the anchor point of the animation into the corner from the
top left corner to the center. This fixes the issue where the preview
appeared to move "up" before following the correct path.

Bug: 149100933
Test: manual; changes animations only
Change-Id: I45edf9a82db5f67efa129bdb8a0fd091189e7c7a
1 file changed