zio-cdev: add missing copyright line

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

zio-cdev.c

+/* Federico Vaga and Alessandro Rubini for CERN, 2011, GNU GPLv2 or later */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>