Properly clear the render target

ScriptableRenderPipeline/HDRenderPipeline/Lighting/Volumetrics/VolumetricLighting.cs

             if (!hasGlobalVolume)
             {
                 // Clear the render target instead of running the shader.
-                CoreUtils.SetRenderTarget(cmd, m_VBufferLightingRT[0]);
+                CoreUtils.SetRenderTarget(cmd, m_VBufferLightingRT[0], ClearFlag.Color, CoreUtils.clearColorAllBlack);
                 return;
             }