user_password_login (Compat) generates a new device regardless if device_id is sent in the post request

[maspling]

Describe the bug
According to https://spec.matrix.org/v1.13/client-server-api/#post_matrixclientv3login , if a device_id is sent in the login request, and it is a previously known device id, the session should be reused and the the same device id should be returned in the response.

Looking at the current relevant code, it doesn't seem like device_id is ever read from the request payload and that a new device is created every time.

To Reproduce
Steps to reproduce the behavior:

1. Create a device by completing login flow.
2. Login again with a the same device_id.
3. Response will be a newly generated device_id

Expected behavior
A new device is not created and the same one is reused.