eventloop: add missing duration_cast

Change-Id: I3a7d99c47b8808e7ac89b194723e605fcc1facdd
Reviewed-on: http://gerrit.aldebaran.lan/48733
Reviewed-by: pdaouadi <pdaouadi@aldebaran-robotics.com>
Tested-by: pdaouadi <pdaouadi@aldebaran-robotics.com>