Linux 3.11 compatibility fix
From: https://github.com/umlaeute/v4l2loopback/commit/cfbbdbb77740eb2484d896a627d0928f24a91aff
and https://github.com/umlaeute/v4l2loopback/commit/108cb697c5b26395da93c3f1331829eea24769f4