nfs/nfs4idmap: avoid pointless reference count bump

The override creds are allocated with a long-term refernce when the
id_resolver is initialized via prepare_kernel_creds() that is put when
the id_resolver is destroyed.

Link: https://lore.kernel.org/r/20241125-work-cred-v2-14-68b9d38bb5b2@kernel.org
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/nfs/nfs4idmap.c

@@ -311,9 +311,9 @@ static ssize_t nfs_idmap_get_key(const char *name, size_t namelen,
 	const struct user_key_payload *payload;
 	ssize_t ret;
 
-	saved_cred = override_creds(get_new_cred(id_resolver_cache));
+	saved_cred = override_creds(id_resolver_cache);
 	rkey = nfs_idmap_request_key(name, namelen, type, idmap);
-	put_cred(revert_creds(saved_cred));
+	revert_creds(saved_cred);
 
 	if (IS_ERR(rkey)) {
 		ret = PTR_ERR(rkey);