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