sparse says:

    fs/ceph/ioctl.c:100:28: warning: cast to restricted __le64

preferred_osd is a __s64 so we don't need to do any conversion. Also,
just remove the cast in ceph_ioctl_get_layout as it's not needed.
Signed-off-by: NJeff Layton <jlayton@redhat.com>
Reviewed-by: NSage Weil <sage@redhat.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>