security: update documentation for security_request_module

Update documentation for security_request_module to indicate
return value, as suggested by Serge Hallyn.
Signed-off-by: NJames Morris <jmorris@namei.org>

include/linux/security.h

@@ -681,6 +681,7 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  * @kernel_module_request:
  *	Ability to trigger the kernel to automatically upcall to userspace for
  *	userspace to load a kernel module with the given name.
+ *	Return 0 if successful.
  * @task_setuid:
  *	Check permission before setting one or more of the user identity
  *	attributes of the current process.  The @flags parameter indicates