Fix typo disabling NPOT on AMD D3D9

BUG=angle:799

Change-Id: Ifd4200774665f22d5f6ed196862192585d0799c0
Reviewed-on: https://chromium-review.googlesource.com/224481
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Shannon Woods <shannonwoods@chromium.org>