creds_are_invalid() needs to be exported for use by modules:

ERROR: "creds_are_invalid" [fs/cachefiles/cachefiles.ko] undefined!
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Morris <jmorris@namei.org>

kernel/cred.c

@@ -799,6 +799,7 @@ bool creds_are_invalid(const struct cred *cred)
 #endif
 	return false;
 }
+EXPORT_SYMBOL(creds_are_invalid);
 
 /*
  * dump invalid credentials