net: hns: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -92,7 +92,7 @@ struct ppe_common_cb {
 	u8 comm_index;   /*ppe_common index*/
 
 	u32 ppe_num;
-	struct hns_ppe_cb ppe_cb[0];
+	struct hns_ppe_cb ppe_cb[];
 
 };
 

drivers/net/ethernet/hisilicon/hns/hns_dsaf_rcb.h

@@ -108,7 +108,7 @@ struct rcb_common_cb {
 	u32 ring_num;
 	u32 desc_num; /*  desc num per queue*/
 
-	struct ring_pair_cb ring_pair_cb[0];
+	struct ring_pair_cb ring_pair_cb[];
 };
 
 int hns_rcb_buf_size2type(u32 buf_size);