Fixed wrong XR namespace in 2017.2

Author: Chman

PostProcessing/Runtime/Utils/RuntimeUtilities.cs

@@ -236,7 +236,7 @@ public static bool isSinglePassStereoEnabled
                     && UnityEditor.PlayerSettings.stereoRenderingPath == UnityEditor.StereoRenderingPath.SinglePass
                     && Application.isPlaying;
 #elif UNITY_2017_2_OR_NEWER
-                return UnityEngine.XRSettings.eyeTextureDesc.vrUsage == VRTextureUsage.TwoEyes;
+                return UnityEngine.XR.XRSettings.eyeTextureDesc.vrUsage == VRTextureUsage.TwoEyes;
 #else
                 return false;
 #endif