Phab: Fix incorrect variable name

Fix a bug with importing Hardware info that can be seen
in task 3160 of https://bugzillapreview.wmflabs.org/ (field is called
platform as per
http://www.bugzilla.org/docs/4.4/en/html/api/Bugzilla/WebService/Bug.html )

Change-Id: I5ce71ba6feb8b823b44db87dc0b0d3fb9de99721