htb: fix values in opt dump

in htb_change_class() cl->buffer and cl->buffer are stored in ns.
So in dump, convert them back to psched ticks.

Note this was introduced by:
commit 56b765b7


    htb: improved accuracy at high rates

Please consider this for -net/-stable.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>