asahi: fix size calculation for 2d msaa arrays

otherwise the hw can overprefetch. fixes KHR-GL42.shader_image_load_store.basic-allTargets-load-ms

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26614>
1 file changed