It seems Jessie repository is reachable but Jessie security updates repository is not. That would be logical since Jessie for the Mips architecture is EOL.
There are no more security updates for your architecture so you only need to comment out the security updates in the /etc/apt/sources.list file in order to avoid the previous error message. Even if Jessie updates (not security updates) is reachable, there are no more updates. So apt-get upgrade won't upgrade anything. And probably when Buster is released, Jessie repositories will be transfered to http://archive.debian.org
