Fixes for Microsoft OS 1.0 descriptor request handler

[martinling]

Fixes the following issues:

• Handler must only claim requests with its specified request code.
• Recipient must be device for index 4, and interface for index 5.
• Don't generate stalls - that's handled by not claiming requests.

Tested with https://github.com/greatscottgadgets/cynthion/pull/94 on Windows 10.