qdisc: fix a module refcount leak in qdisc_create_dflt()

Should qdisc_alloc() fail, we must release the module refcount
we got right before.

Fixes: 6da7c8fc ("qdisc: allow setting default queuing discipline")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>