Updated poller/discovery forms to use validate_device_id function

This in reference to the request in:

https://github.com/librenms/librenms/pull/239#event-135262233

Ref : https://scrutinizer-ci.com/g/librenms/librenms/inspections/c2cf9f29-66b5-4fcd-b131-57b6ae74a6b1/issues/files/html/forms/discovery-module-update.inc.php?status=new&orderField=path&order=asc