asahi: Fix rendering into mipmapped framebuffers
batch->key.width will be minified, but then the PBE::level field will incorrectly minify again.
Fixes dEQP-GLES31.functional.shaders.framebuffer_fetch.basic.framebuffer_texture_level
Signed-off-by: Alyssa Rosenzweig alyssa@rosenzweig.io