Fix typo in mpu.exe parameters binding

[skondratov]

Hi!

Here is simple typo and also i found one more mpu.exe bug:

I get 'Process is terminated due to StackOverflowException.' when trying to prepare serializer for something like:

   class Example
   {
       public Example[] Childs; 
   } 

I know what it is in this function: https://github.com/msgpack/msgpack-cli/blob/20ae0c36d292c3f6f51248872e362170fcaf36d4/src/MsgPack/Serialization/SerializerGenerator.cs#L498

But it is so tangled.. i gave up trying to refactor it. I would completely remove it and write again.. But i need more time to understand the logic. You possibly see less radical solution.

[skondratov]

I suppose build was broken before my changes.

[yfakariya]

I agree the build failure was caused before your commit. I'll fix it soon. Thank you!