Use access to backing field on overridden property with private setter

#KT-27772 Fixed

compiler/testData/codegen/box/properties/privateAccessorOfOverriddenProperty.kt

@@ -0,0 +1,18 @@
+interface A {
+    val foo: String
+}
+
+class B : A {
+    override var foo: String = "Fail"
+        private set
+
+    fun setOK(other: B) {
+        other.foo = "OK"
+    }
+}
+
+fun box(): String {
+    val b = B()
+    b.setOK(b)
+    return b.foo
+}