vulkan: add DXT23_SRGB

src/video_core/renderer_vulkan/maxwell_to_vk.cpp

@@ -164,7 +164,7 @@ struct FormatTuple {
     {vk::Format::eUndefined, {}},                                // ASTC_2D_5X4
     {vk::Format::eUndefined, {}},                                // BGRA8_SRGB
     {vk::Format::eBc1RgbaSrgbBlock, {}},                         // DXT1_SRGB
-    {vk::Format::eUndefined, {}},                                // DXT23_SRGB
+    {vk::Format::eBc2SrgbBlock, {}},                             // DXT23_SRGB
     {vk::Format::eBc3SrgbBlock, {}},                             // DXT45_SRGB
     {vk::Format::eBc7SrgbBlock, {}},                             // BC7U_SRGB
     {vk::Format::eR4G4B4A4UnormPack16, Attachable},              // R4G4B4A4U