net: hns: dereference ppe_cb->ppe_common_cb if it is non-null

ppe_cb->ppe_common_cb is being dereferenced before a null check is
being made on it.  If ppe_cb->ppe_common_cb is null then we end up
with a null pointer dereference when assigning dsaf_dev.  Fix this
by moving the initialisation of dsaf_dev once we know
ppe_cb->ppe_common_cb is OK to dereference.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Yisen Zhuang <yisen.zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>