Make cloud switch entity `_update_state` function a coro

Description

Make the _update_state function of the cloud switch entities a coro.

Motivation and Context

The async_listen_updates of the cloud client requires the function to be a coro, as the function uses the async_create_catching_coro logging helper of core, which (in some nested functions) always awaits.

How has this been tested?

This appeared while beta testing https://github.com/home-assistant/core/issues/111797. I applied this change on my prod system and the log went away.

Screenshots (if appropriate):

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Other

Checklist

[x] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.

frenck / spook

Make cloud switch entity `_update_state` function a coro #647