[dxgi] Allow creating R16_SFLOAT views for D16_UNORM images

Just use R16_UNORM. For some reason, D3D11 actually allows this, and
Trine 4 wants the corresponding calls to succeed, although we're going
to interpret the data as UNORM rather than FLOAT.

src/dxgi/dxgi_format.cpp

@@ -263,7 +263,7 @@ namespace dxvk {
       VK_FORMAT_R16_UINT },
     // DXGI_FORMAT_R16_FLOAT
     { VK_FORMAT_R16_SFLOAT,
-      VK_FORMAT_UNDEFINED,
+      VK_FORMAT_D16_UNORM,
       VK_FORMAT_R16_UINT,
       VK_IMAGE_ASPECT_COLOR_BIT },
     // DXGI_FORMAT_D16_UNORM