pkt_sched: sch_htb: Clean htb_class prio and quantum fields

While implementing htb_parent_to_leaf() there where added backup prio
and quantum struct htb_class fields to preserve these values for inner
classes in case of their return to leaf. This patch cleans this a bit
by removing union leaf duplicates.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>