net: sched: fix error path in tcf_proto_create() when modules are not configured

In case modules are not configured, error out when tp->ops is null
and prevent later null pointer dereference.

Fixes: 33a48927 ("sched: push TC filter protocol creation into a separate function")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>