vulkan: Fix oversights in V6 of android native buffer

- We want a *Flags, not a *FlagBits here.
- Header failed to declare the VK_STRUCTURE_TYPE enum, although it was
  declared in api file.

  Found by trying to actually use this.

Test: build
Change-Id: I656b6095a428c116b769073d825c747aff24d12b
diff --git a/vulkan/api/vulkan.api b/vulkan/api/vulkan.api
index 12fc935..df45c20 100644
--- a/vulkan/api/vulkan.api
+++ b/vulkan/api/vulkan.api
@@ -2900,7 +2900,7 @@
 class VkSwapchainImageCreateInfoANDROID {
     VkStructureType                             sType
     const void*                                 pNext
-    VkSwapchainImageUsageFlagBitsANDROID        flags
+    VkSwapchainImageUsageFlagsANDROID           flags
 }
 
 @extension("VK_GOOGLE_display_timing")