Staging: lustre: obdclass: Declare structure as static.

Declare structure as static since it is not accessed anywhere
apart from this particular file.

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>