hasvk: Neutralize the unwritten chroma with monochrome video.

Otherwise we sample garbage with, say, yuvj420p.

Assisted-by: Claude

src/intel/vulkan_hasvk/anv_private.h

@@ -3211,6 +3211,8 @@ struct anv_image {
     */
    bool from_gralloc;
 
+   bool vid_neutral_chroma_init;
+
    /**
     * The memory bindings created by vkCreateImage and vkBindImageMemory.
     *