fix mariadb template call

I got this error when I tried to install/upgrade nextcloud from master:

Error: UPGRADE FAILED: template: nextcloud-onlyoffice/templates/job-setup-apps.yaml:32:17: executing "nextcloud-onlyoffice/templates/job-setup-apps.yaml" at <include "nextcloud-onlyoffice.env" .>: error calling include: template: nextcloud-onlyoffice/charts/nextcloud/charts/mariadb/templates/_helpers.tpl:4:7: executing "mariadb.primary.fullname" at <eq .Values.architecture "replication">: error calling eq: incompatible types for comparison

It's because Nextcloud stopped including mariadb.fullname in their templates. That's because we can now use templates in a subchart context as I did in this branch.