staging: lustre: obd: make echo_lock_ops const

Declare echo_lock_ops object of type cl_lock_operations as const as it
is only passed to the function cl_lock_slice_add. The corresponding
argument is of type const, so make the object const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>