dawn/native/d3d12: use correct __uuidof operator

This code uses `_uuidof` (single undescore) instead of `__uuidof`
(two underscores), only the latter is documented as the officially
supported operator by Microsoft:

https://docs.microsoft.com/en-us/cpp/cpp/uuidof-operator?view=msvc-170

I suspect `_uuidof` and `__uuidof` are the same under the msvc compiler,
but in other compilers (Zig/clang/MinGW) only the officially supported
`__uuidof` is exposed. This change improves compatability with such
compilers.

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
Change-Id: If2850a1a98507161739fcd5f52ebd4ceaefffe75
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/87309
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/dawn/native/d3d12/AdapterD3D12.cpp

@@ -67,7 +67,7 @@ MaybeError Adapter::InitializeImpl() {
     // rendering.
     const PlatformFunctions* functions = GetBackend()->GetFunctions();
     if (FAILED(functions->d3d12CreateDevice(GetHardwareAdapter(), D3D_FEATURE_LEVEL_11_0,
-                                            _uuidof(ID3D12Device), &mD3d12Device))) {
+                                            __uuidof(ID3D12Device), &mD3d12Device))) {
         return DAWN_INTERNAL_ERROR("D3D12CreateDevice failed");
     }