fcc_submitter: fix a regression from previous commit

There is a previous commit causes fcc_submitter does not store linkinfo
package information to data list, this causes fcc_submitter fails to
find the main-package information.

fcc_submitter.py

@@ -255,7 +255,7 @@ class FccSubmitter(object):
         root = ET.fromstring(http_GET(url).read())
         data = {}
         linkinfo = root.find('linkinfo')
-        if linkinfo:
+        if linkinfo is not None:
             data['linkinfo'] = linkinfo.attrib['package']
         else:
             data['linkinfo'] = None