eve-file: set event_type to fileinfo

To remain constistent with the other logs, set the event type to
the same name as the structure containing the defails. In this
case fileinfo.

Part of bug #1127. https://redmine.openinfosecfoundation.org/issues/1127

- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/229
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/149