llvmpipe: pass layer count to rast clear

this otherwise passes the fb layer, which is not quite right when
using multiview with view indexing

cc: mesa-stable

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33632>

src/gallium/drivers/llvmpipe/lp_rast.c

@@ -168,7 +168,7 @@ lp_rast_clear_color(struct lp_rasterizer_task *task,
                     0,
                     task->width,
                     task->height,
-                    scene->fb_max_layer + 1,
+                    scene->cbufs[cbuf].layer_count,
                     &uc);
    }
 

src/gallium/drivers/llvmpipe/lp_scene.c

@@ -181,6 +181,7 @@ init_scene_texture(struct lp_scene_surface *ssurf, struct pipe_surface *psurf)
       assert(ssurf->map);
       ssurf->format_bytes = util_format_get_blocksize(psurf->format);
       ssurf->nr_samples = util_res_sample_count(psurf->texture);
+      ssurf->layer_count = psurf->u.tex.last_layer - psurf->u.tex.first_layer + 1;
    } else {
       struct llvmpipe_resource *lpr = llvmpipe_resource(psurf->texture);
       unsigned pixstride = util_format_get_blocksize(psurf->format);

src/gallium/drivers/llvmpipe/lp_scene.h

@@ -127,6 +127,7 @@ struct lp_scene_surface {
    unsigned format_bytes;
    unsigned sample_stride;
    unsigned nr_samples;
+   unsigned layer_count;
 };