virtio_net: fix error return code in virtnet_probe()

Fix to return a negative error code from the failover create fail error
handling case instead of 0, as done elsewhere in this function.

Fixes: ba5e4426 ("virtio_net: Extend virtio to use VF datapath when available")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>