panfrost: mark two variables as unused

The variables are currently unused as panvk does not support
SSBOs yet.

Silences a compile warning with clang

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14790>

src/panfrost/vulkan/panvk_descriptor_set.c

@@ -202,7 +202,8 @@ panvk_GetDescriptorSetLayoutSupport(VkDevice _device,
       return;
    }
 
-   unsigned sampler_idx = 0, tex_idx = 0, ubo_idx = 0, ssbo_idx = 0, dynoffset_idx = 0;
+   unsigned sampler_idx = 0, tex_idx = 0, ubo_idx = 0, UNUSED ssbo_idx = 0,
+      UNUSED dynoffset_idx = 0;
    for (unsigned i = 0; i < pCreateInfo->bindingCount; i++) {
       const VkDescriptorSetLayoutBinding *binding = &bindings[i];