LeakingThisInspection: fix false positives for enum class

#KT-25905 Fixed

idea/testData/inspectionsLocal/leakingThis/enumEntryHasOverriddenMember5.kt

@@ -0,0 +1,13 @@
+// PROBLEM: Accessing non-final property x in constructor
+// FIX: none
+enum class Foo : Bar {
+    ONE {
+        override val x = 1
+    };
+
+    val double = x<caret>
+}
+
+interface Bar {
+    val x: Int
+}