octeon_ep: ensure octep_get_link_status() successfully before octep_link_up()

octep_get_link_status() can fail because send mbox message failed, then
octep_get_link_status() will return ret less than 0. Excute octep_link_up()
as long as ret is not equal to 0 in octep_open() now. That is not correct.

The value type of link.state is enum octep_ctrl_net_state. Positive value
represents up. Excute octep_link_up() when ret is bigger than 0.

Fixes: 862cd659

 ("octeon_ep: Add driver framework and device initialization")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>