fix: [mariabd] bad typo would prevent dump to be made

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

mariadb/hooks/schedule_command-relation-joined

@@ -38,6 +38,6 @@ $schedule   root lock $label -D -p 10 -c "\
         -v \"$HOST_CHARM_STORE/${CHARM_REL_PATH#${CHARM_STORE}/}/resources/bin/mysql-backup:/usr/sbin/mysql-backup\" \
         -v \"$SERVICE_DATASTORE/var/backups/mysql:/var/backups/mysql\" \
         --entrypoint mysql-backup \
-        \"$DOCKER_BASE_IMAGE\" --host \"${SERVICE_IMAGE}\"" 2>&1 | ts '\%F \%T \%Z' >> /var/log/cron/${label}_script.log
+        \"$DOCKER_BASE_IMAGE\" --host \"${SERVICE_NAME}\"" 2>&1 | ts '\%F \%T \%Z' >> /var/log/cron/${label}_script.log
 EOF
 chmod +x "$DST"