Fix matrix_corporal_docker_image_name_prefix referencing matrix_synapse_ stuff

roles/matrix-corporal/defaults/main.yml

@@ -23,7 +23,7 @@ matrix_corporal_container_extra_arguments: []
 matrix_corporal_systemd_required_services_list: ['docker.service']
 
 matrix_corporal_docker_image: "{{ matrix_corporal_docker_image_name_prefix }}devture/matrix-corporal:{{ matrix_corporal_docker_image_tag }}"
-matrix_corporal_docker_image_name_prefix: "{{ 'localhost/' if matrix_synapse_container_image_self_build else 'docker.io/' }}"
+matrix_corporal_docker_image_name_prefix: "{{ 'localhost/' if matrix_corporal_container_image_self_build else 'docker.io/' }}"
 matrix_corporal_docker_image_tag: "1.11.0"
 matrix_corporal_docker_image_force_pull: "{{ matrix_corporal_docker_image.endswith(':latest') }}"