LeakingThisInspection: fix false positives for enum class

#KT-25905 Fixed

idea/testData/inspectionsLocal/leakingThis/enumEntryHasOverriddenMember6.kt

@@ -0,0 +1,11 @@
+// PROBLEM: none
+// FIX: none
+enum class Foo : Bar {
+    ONE;
+
+    val double = x<caret>
+}
+
+interface Bar {
+    val x: Int get() = 42
+}