[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/codegen/box/delegatedProperty/optimizedDelegatedProperties/mixedArgumentSizes.kt

@@ -1,6 +1,5 @@
 // !LANGUAGE: -NewInference
 
-// IGNORE_BACKEND_FIR: JVM_IR
 inline operator fun Double.provideDelegate(thisRef: Any?, kProp: Any?) = this.toLong()
 
 inline operator fun Long.getValue(thisRef: Any?, kProp: Any?) = this.toInt()
@@ -59,4 +58,4 @@ fun box(): String {
     x.test(intArray)
     
     return "OK"
-}
+}