d3d11: Fix debug build on UWP

d3d11: Fix debug build on UWP

GstDXGIGetDebugInterface() is unused when targeting UWP. We directly
call DXGIGetDebugInterface1() in that case.

Fixes build failure:

../gst-libs/gst/d3d11/gstd3d11device.cpp(271): error C2440: '=': cannot convert from 'HRESULT (__cdecl *)(UINT,const IID &,void **)' to 'DXGIGetDebugInterface_t'
../gst-libs/gst/d3d11/gstd3d11device.cpp(271): note: This conversion requires a reinterpret_cast, a C-style cast or function-style cast

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3118>