I was facing the same issue. The problem was on your github repo , you might be using some old ssh key.
You need to update the current ssh key.
Steps involved are:
1. vim ~/.ssh/id_rsa.pub
2. copy the ssh key
3. Go to the github settings
4. Select the option ssh keys
5. Remove the old ssh keys not used anymore.
6. Add a new ssh key.
7. Try running the "git submodule update --recursive"
This worked for me !!