FramebufferAttachment: Cast pointers directly. Instead of using a temporary pointer-to-pointer, try casting the pointer-to-pointer type directly. This will facilitate Vulkan's use of RenderTargets. BUG=angleproject:1319 Change-Id: I0a14762e8e442b9eaa6eba3fdf653aef3c362533 Reviewed-on: https://chromium-review.googlesource.com/424148 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>