Fix sRGB backbuffers on the SDL_GPU backend

Author: kg

src/FNA3D_Driver_SDL.c

@@ -2651,7 +2651,12 @@ static void SDLGPU_ResetBackbuffer(
 		presentationParameters
 	);
 
-	swapchainComposition = SDL_GPU_SWAPCHAINCOMPOSITION_SDR;
+	swapchainComposition = (
+		(presentationParameters->backBufferFormat == FNA3D_SURFACEFORMAT_COLORSRGB_EXT) ||
+		(presentationParameters->backBufferFormat == FNA3D_SURFACEFORMAT_COLORBGRA_EXT)
+	)
+		? SDL_GPU_SWAPCHAINCOMPOSITION_SDR_LINEAR
+		: SDL_GPU_SWAPCHAINCOMPOSITION_SDR;
 
 	if (SDL_GetHintBoolean("FNA3D_ENABLE_HDR_COLORSPACE", false))
 	{