NFC: 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 7649773293 ("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/nfc/fdp/fdp.c

@@ -76,7 +76,7 @@ static u8 nci_core_get_config_otp_ram_version[5] = {
 struct nci_core_get_config_rsp {
 	u8 status;
 	u8 count;
-	u8 data[0];
+	u8 data[];
 };
 
 static int fdp_nci_create_conn(struct nci_dev *ndev)

drivers/nfc/st21nfca/dep.c

@@ -66,7 +66,7 @@ struct st21nfca_atr_req {
 	u8 bsi;
 	u8 bri;
 	u8 ppi;
-	u8 gbi[0];
+	u8 gbi[];
 } __packed;
 
 struct st21nfca_atr_res {
@@ -79,7 +79,7 @@ struct st21nfca_atr_res {
 	u8 bri;
 	u8 to;
 	u8 ppi;
-	u8 gbi[0];
+	u8 gbi[];
 } __packed;
 
 struct st21nfca_psl_req {