sch_tbf: Fix potential memory leak in tbf_change().

sch_tbf: Fix potential memory leak in tbf_change().

[ Upstream commit 724b9e1d75ab3401aaa081bd4efb440c1b3509db ]

The allocated child qdisc is not freed in error conditions.
Defer the allocation after user configuration turns out to be
valid and acceptable.

Fixes: cc106e441a63b ("net: sched: tbf: fix the calculation of max_size")
Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>