Look into proper context when generating backing field access

Problem manifests when a class property name matches a companion object
property name, and class property is referenced in closure context.

 #KT-19367 Fixed Target versions 1.1.5

compiler/testData/codegen/box/classes/comanionObjectFieldVsClassField.kt

@@ -0,0 +1,15 @@
+// WITH_RUNTIME
+
+class Host {
+    val ok = "OK"
+
+    fun foo() = run { bar(ok) }
+
+    companion object {
+        val ok = 0
+
+        fun bar(s: String) = s.substring(ok)
+    }
+}
+
+fun box() = Host().foo()