[FIR] Fix generating this reference in delegated accessors

There was a problem with delegated extension property with dispatch
  receiver that `this` in `getValue` call was set to dispatch receiver
  instead of extension one

compiler/testData/ir/irText/declarations/provideDelegate/memberExtension.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 object Host {
     class StringDelegate(val s: String) {
         operator fun getValue(receiver: String, p: Any) = receiver + s