zink: more accurately check samplecount caps for shader images
lavapipe can only do up to 4bits, so this isn't just a binary check
Fixes: 0daa6155 ("zink: check if multisample support exists for shader image formats")
lavapipe can only do up to 4bits, so this isn't just a binary check
Fixes: 0daa6155 ("zink: check if multisample support exists for shader image formats")