vulkan/runtime: only set shader subgroup info if non-zero

Signed-off-by: Simon Perretta <simon.perretta@imgtec.com>
Fixes: 67c4b762a5 ("vulkan: setup max_subgroup_size for drivers without var...")
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37533>

src/vulkan/runtime/vk_pipeline.c

@@ -120,7 +120,7 @@ vk_set_subgroup_size(struct vk_device *device,
       shader->info.min_subgroup_size = req_subgroup_size;
    } else if (allow_varying || spirv_version >= 0x10600) {
       /* Starting with SPIR-V 1.6, varying subgroup size is the default */
-   } else {
+   } else if (properties->subgroupSize) {
       shader->info.api_subgroup_size = properties->subgroupSize;
       shader->info.max_subgroup_size = properties->subgroupSize;
       if (require_full) {