staging: lustre: obdecho: constify lu_device_operations and cl_device_operations structures

These lu_device_operations and cl_device_operations structures are never
modified, so declare them as const.  Other structures of these types are
already const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>