net: hns3: fix null pointer dereference before null check

pointer ndev is being dereferenced with the call to netif_running
before it is being null checked.  Re-order the code to only dereference
ndev after it has been null checked.

Detected by CoverityScan, CID#1457206 ("Dereference before null check")

Fixes: 9df8f79a ("net: hns3: Add DCB support when interacting with network stack")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>