82231fd74d mentioned that for the "rot"
transform flip=true must be set, which "makes no sense at all".
The reason this is happening is that the rotation matrix calculation
is only valid for the 2D coordinate system where y axis is 90 degrees
counterclockwise from x axis, but the coordinate system of chroma
offset has its origin at top-left so it is the opposite, which results
in the rotation going to the opposite way. Setting flip=true fixes the
rotation direction, but results in a flipped y coordinate.
Fix this by reversing the rotation angle for chroma offset rotation
matrix calculation. This also allows removing some duplicated code.
ca7aeb71ee