net: openvswitch: conntrack: simplify the return expression of ovs_ct_limit_get_default_limit()

Simplify the return expression.

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Reviewed-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>