D3D11: Fix ClearBufferiv with STENCIL. For some reason we were using the second GLint value passed into the method, when the spec says we should have a single clear value. Noticed when adding tests for lazy robust resource init (tests will be added in a subsequent patch). BUG=angleproject:2107 Change-Id: Iadfc5072796255072bfb71ff1918253045e29576 Reviewed-on: https://chromium-review.googlesource.com/675049 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>