net: ethernet: nb8800: fix error return code in nb8800_open()

Fix to return error code -ENODEV from the of_phy_connect() error
handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: David S. Miller <davem@davemloft.net>