staging: lustre: Use const static file_operations struct

This commit corrects the following sparse warning regarding a
file_operations structure being non-static and constifies the
structure in question as well.

  warning: symbol 'lprocfs_stats_seq_fops' was not declared.
    Should it be static?

Signed-off-by: M. Vefa Bicakci <m.v.b@runbox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>