You should have received a tarball containing the SSH private key to use for accessing your kernel.org account. Place that private key into your ~/.ssh directory, e.g.:

cp korg-username ~/.ssh/id_rsa_korg

Add the following entry into your .ssh/config:

Host gitolite.kernel.org
  User git
  IdentityFile ~/.ssh/id_rsa_korg
  IdentitiesOnly yes