FIX: Bastion undefined variable (#7227)

Fixes the following error when using Bastion Node with the sample config.
```
fatal: [bastion]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'dict object' has no attribute 'bastion'\n\nThe error appears to be in '/home/felix/inovex/kubespray/roles/bastion-ssh-config/tasks/main.yml': line 2, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n---\n- name: set bastion host IP\n  ^ here\n"}
```