net: hns: enet specifies a reference to dsaf

This patch replace the assoication between dsaf and enet from string
matching to object reference. It requires the DTS to be updated within
BIOS. Thanks god it can be done for all released boards.

Signed-off-by: Kejian Yan <yankejian@huawei.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Yisen Zhuang <yisen.zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>