Fix validation warning in VK_Indirect

VUID-VkDrawIndexedIndirectCommand-firstInstance-00554
If the drawIndirectFirstInstance feature is not enabled, firstInstance must be 0

util/test/demos/vk/vk_indirect.cpp

@@ -104,6 +104,7 @@ void main()
     optDevExts.push_back(VK_KHR_DRAW_INDIRECT_COUNT_EXTENSION_NAME);
 
     features.multiDrawIndirect = VK_TRUE;
+    features.drawIndirectFirstInstance = VK_TRUE;
 
     VulkanGraphicsTest::Prepare(argc, argv);