staging: gdm72xx: add userspace data struct

This fixes the sparse warnings about dereferencing a userspace pointer.

Once I updated the sparse annotations, I noticed a bug in
gdm_wimax_ioctl() where we pass a user space pointer to gdm_update_fsm()
which dereferences it. I fixed this.

Signed-off-by: Wim de With <nauxuron@wimdewith.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>