rtw89: core.h: Replace zero-length array with flexible-array member

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220216195047.GA904198@embeddedor

drivers/net/wireless/realtek/rtw89/core.h

@@ -2879,7 +2879,7 @@ struct rtw89_dev {
 	int napi_budget_countdown;
 
 	/* HCI related data, keep last */
-	u8 priv[0] __aligned(sizeof(void *));
+	u8 priv[] __aligned(sizeof(void *));
 };
 
 static inline int rtw89_hci_tx_write(struct rtw89_dev *rtwdev,