staging: comedi: fix infoleak to userspace

BugLink: http://bugs.launchpad.net/bugs/823296

commit 819cbb120eaec7e014e5abd029260db1ca8c5735 upstream.

driver_name and board_name are pointers to strings, not buffers of size
COMEDI_NAMELEN.  Copying COMEDI_NAMELEN bytes of a string containing
less than COMEDI_NAMELEN-1 bytes would leak some unrelated bytes.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>