[ubuntu] Fix missing return in ubuntu policy

Ubuntu policy is missing a `return`  in `get_upload_url()` method that
causes the upload to be implictly disabled when `--upload-url` is
specified.

Closes: #3183
Signed-off-by: Chi Wai, Chan <chiwai.chan@canonical.com>

sos/policies/distros/ubuntu.py

@@ -78,6 +78,6 @@ def get_upload_url(self):
                 return self._upload_url
             fname = os.path.basename(self.upload_archive_name)
             return self._upload_url + fname
-        super(UbuntuPolicy, self).get_upload_url()
+        return super(UbuntuPolicy, self).get_upload_url()
 
 # vim: set et ts=4 sw=4 :