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>

drivers/net/ethernet/hisilicon/hns/hns_dsaf_ppe.c

@@ -328,9 +328,10 @@ static void hns_ppe_init_hw(struct hns_ppe_cb *ppe_cb)
 static void hns_ppe_uninit_hw(struct hns_ppe_cb *ppe_cb)
 {
 	u32 port;
-	struct dsaf_device *dsaf_dev = ppe_cb->ppe_common_cb->dsaf_dev;
 
 	if (ppe_cb->ppe_common_cb) {
+		struct dsaf_device *dsaf_dev = ppe_cb->ppe_common_cb->dsaf_dev;
+
 		port = ppe_cb->index;
 		dsaf_dev->misc_op->ppe_srst(dsaf_dev, port, 0);
 	}