thermal: int340x: Clean up _OSC context init

Now that the UUID is already sanitized by the caller,
lets trivially clean up some of the context arming.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Zhang Rui <rui.zhang@intel.com>
[ rjw: Subject edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>