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

fs/open.c

@@ -442,7 +442,8 @@ static const struct cred *access_override_creds(void)
 	 * 'get_current_cred()' function), that will clear the
 	 * non_rcu field, because now that other user may be
 	 * expecting RCU freeing. But normal thread-synchronous
-	 * cred accesses will keep things non-RCY.
+	 * cred accesses will keep things non-racy to avoid RCU
+	 * freeing.
 	 */
 	override_cred->non_rcu = 1;