docs: more doxygen fixes (#2736)

src/platform/windows/display_ram.cpp

@@ -370,6 +370,9 @@ namespace platf::dxgi {
     return 0;
   }
 
+  /**
+   * @memberof platf::dxgi::display_ram_t
+   */
   int
   display_ram_t::dummy_img(platf::img_t *img) {
     if (complete_img(img, true)) {

src/platform/windows/display_vram.cpp

@@ -1583,6 +1583,9 @@ namespace platf::dxgi {
   }
 
   // This cannot use ID3D11DeviceContext because it can be called concurrently by the encoding thread
+  /**
+   * @memberof platf::dxgi::display_vram_t
+   */
   int
   display_vram_t::dummy_img(platf::img_t *img_base) {
     return complete_img(img_base, true);