D3D11 FL9_3: Fix bug in R32F vertex format emulation. We would allow direct storage when this format is emulated. Noticed this when making a test which used a single float vertex format. BUG=angleproject:1635 Change-Id: Ia2164b0f311b27f24b6aa7760eb9f9a3834c6044 Reviewed-on: https://chromium-review.googlesource.com/451578 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>