fs: Clarify "non-RCY" in access_override_creds() comment

The term is originally intended as a joke that stands for "non-racy".
This trips new contributors who mistake it for RCU typo [1].

Replace the term with more-explicit wording.

Link: https://lore.kernel.org/r/20231030-debatten-nachrangig-f58abcdac530@brauner/


Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20231031114728.41485-1-bagasdotme@gmail.com


Signed-off-by: Christian Brauner <brauner@kernel.org>