KEYS: Fix default security_session_to_parent()

Fix the default security_session_to_parent() in linux/security.h to have a
body.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/security.h b/include/linux/security.h
index f4eb32d..10a09257 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2988,7 +2988,10 @@
 
 static inline int security_key_session_to_parent(const struct cred *cred,
 						 const struct cred *parent_cred,
-						 struct key *key);
+						 struct key *key)
+{
+	return 0;
+}
 
 #endif
 #endif /* CONFIG_KEYS */