HDRenderPipeline: add setter for scene settings

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/SceneSettings.cs

     {
         public CommonSettings commonSettings
         {
+            set { m_CommonSettings = value; }
+            set { m_SkySettings = value; }
+            set { m_SsaoSettings = value; }
             get { return m_SsaoSettings; }
         }