rusticl/image: take pitches into account when allocating memory for maps
This is more correct than the previous code and the CL CTS relies on edge case behavior here, e.g. for 1Dbuffer images. I think part of that is not actually required by the spec, but whatever. Fixes: 7b22bc61 ("rusticl/memory: complete rework on how mapping is implemented") Part-of: <mesa/mesa!30528>