test/binding: inherit Sampler from NonDispHandle

This also assumes VkSampler does not require any VkDeviceMemory.
diff --git a/tests/vkrenderframework.cpp b/tests/vkrenderframework.cpp
index 8f3eeeb..e66384b 100644
--- a/tests/vkrenderframework.cpp
+++ b/tests/vkrenderframework.cpp
@@ -466,7 +466,7 @@
     m_type_counts.push_back(tc);
 
     VkDescriptorInfo tmp = texture->m_descriptorInfo;
-    tmp.sampler = sampler->obj();
+    tmp.sampler = sampler->handle();
     m_imageSamplerDescriptors.push_back(tmp);
 
     m_writes.push_back(vk_testing::Device::write_descriptor_set(vk_testing::DescriptorSet(),