Fix proxy volumes for sphere

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Reflection/PlanarReflectionProbe.cs

             get
             {
                 return m_ProxyVolumeReference != null
-                    ? m_ProxyVolumeReference.proxyVolume.boxSize * 0.5f
+                    ? m_ProxyVolumeReference.proxyVolume.extents
                     : influenceVolume.boxBaseSize;
             }
         }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Reflection/ProbeWrapper.cs

             get
             {
                 return additional.proxyVolumeComponent != null
-                    ? additional.proxyVolumeComponent.proxyVolume.boxSize * 0.5f
+                    ? additional.proxyVolumeComponent.proxyVolume.extents
                     : influenceExtents;
             }
         }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Reflection/Volumes/ProxyVolume.cs

         public Vector3 sphereOffset { get { return m_SphereOffset; } set { m_SphereOffset = value; } }
         public bool sphereInfiniteProjection { get { return m_SphereInfiniteProjection; } }
 
+        public Vector3 extents
+        {
+            get
+            {
+                switch (shapeType)
+                {
+                    case ShapeType.Box: return m_BoxSize * 0.5f;
+                    case ShapeType.Sphere: return Vector3.one * m_SphereRadius;
+                    default: return Vector3.one;
+                }
+            }
+        }
+
         public bool infiniteProjection
         {
             get