FIR: Fix case when smartcast receiver is used for call to private method

^KT-54432 Fixed

compiler/testData/codegen/box/smartCasts/avoidSmartCastToDerivedForPrivate.kt

@@ -0,0 +1,16 @@
+open class Base {
+    fun foo(): String {
+        return when (this) {
+            is Derived -> baz()
+            else -> "fail 1"
+        }
+    }
+
+    private fun baz(): String = "OK"
+}
+
+class Derived : Base()
+
+fun box(): String {
+    return Derived().foo()
+}