toshiba: 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/toshiba/ps3_gelic_net.h

@@ -308,7 +308,7 @@ struct gelic_port {
 	struct gelic_card *card;
 	struct net_device *netdev;
 	enum gelic_port_type type;
-	long priv[0]; /* long for alignment */
+	long priv[]; /* long for alignment */
 };
 
 static inline struct gelic_card *port_to_card(struct gelic_port *p)

drivers/net/ethernet/toshiba/ps3_gelic_wireless.h

@@ -158,7 +158,7 @@ struct gelic_eurus_scan_info {
 	__be32 reserved2;
 	__be32 reserved3;
 	__be32 reserved4;
-	u8 elements[0]; /* ie */
+	u8 elements[]; /* ie */
 } __packed;
 
 /* the hypervisor returns bbs up to 16 */

drivers/net/ethernet/toshiba/spider_net.h

@@ -470,7 +470,7 @@ struct spider_net_card {
 	struct spider_net_extra_stats spider_stats;
 
 	/* Must be last item in struct */
-	struct spider_net_descr darray[0];
+	struct spider_net_descr darray[];
 };
 
 #endif

drivers/net/ethernet/toshiba/tc35815.c

@@ -367,7 +367,7 @@ struct TxFD {
 
 struct RxFD {
 	struct FDesc fd;
-	struct BDesc bd[0];	/* variable length */
+	struct BDesc bd[];	/* variable length */
 };
 
 struct FrFD {