winsys/radeon: fix the scratch buffer on gfx6-7

I'm sure this was broken.

Fixes: 1bf39b1f9d - ac,radeonsi: rework how scratch_waves is used and move it to ac_gpu_info.c

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23221>

src/gallium/winsys/radeon/drm/radeon_drm_winsys.c

@@ -566,6 +566,13 @@ static bool do_winsys_init(struct radeon_drm_winsys *ws)
    ws->info.spi_cu_en = 0xffff;
    ws->info.never_stop_sq_perf_counters = false;
 
+   /* The maximum number of scratch waves. The number is only a function of the number of CUs.
+    * It should be large enough to hold at least 1 threadgroup. Use the minimum per-SA CU count.
+    */
+   const unsigned max_waves_per_tg = 1024 / 64; /* LLVM only supports 1024 threads per block */
+   ws->info.max_scratch_waves = MAX2(32 * ws->info.min_good_cu_per_sa * ws->info.max_sa_per_se *
+                                     ws->info.num_se, max_waves_per_tg);
+
    ws->check_vm = strstr(debug_get_option("R600_DEBUG", ""), "check_vm") != NULL ||
                                                                             strstr(debug_get_option("AMD_DEBUG", ""), "check_vm") != NULL;
    ws->noop_cs = debug_get_bool_option("RADEON_NOOP", false);