panvk: Set .is_blit=true when compiling preload shaders

Preload shaders are blit shaders.

Fixes: 0bc3502ca3 ("panvk: Implement a custom FB preload logic")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31678>

src/panfrost/vulkan/panvk_vX_cmd_fb_preload.c

@@ -173,6 +173,7 @@ get_preload_shader(struct panvk_device *dev,
    struct panfrost_compile_inputs inputs = {
       .gpu_id = phys_dev->kmod.props.gpu_prod_id,
       .no_ubo_to_push = true,
+      .is_blit = true,
    };
 
    pan_shader_preprocess(nir, inputs.gpu_id);