staging/lustre/obdclass: use static const for seq_operations

lprocfs_stats_seq_sops is only used in static int lprocfs_stats_seq_open
with seq_open as const struct seq_operations *

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peng Tao <bergwolf@gmail.com>
Cc: devel@driverdev.osuosl.org
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>