radv: Allocate buffer list for MUTABLE descriptor types as well.

Fixes: 86644b84b9 ("radv: Implement VK_VALVE_mutable_descriptor_type.")
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10132>

src/amd/vulkan/radv_descriptor_set.c

@@ -242,6 +242,7 @@ radv_CreateDescriptorSetLayout(VkDevice _device, const VkDescriptorSetLayoutCrea
                                                      &mutable_size, &mutable_align);
          assert(mutable_size && mutable_align);
          set_layout->binding[b].size = mutable_size;
+         binding_buffer_count = 1;
          alignment = mutable_align;
          break;
       }