wifi: ath10k: use flexible array in struct wmi_host_mem_chunks

Currently struct wmi_host_mem_chunks defines:
	struct host_memory_chunk items[1];

Per the guidance in [1] this should be a flexible array. However there
is a documented requirement:
	some fw revisions require at least 1 chunk regardless of count

To satisfy this requirement, follow the guidance from [2] and wrap the
array in a union which contains both the flexible array and a single
instance of the underlying struct. Since the footprint of the struct
is unchanged, no additional driver changes are required.

No functional changes, compile tested only.

[1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
[2] https://lore.kernel.org/linux-wireless/202308301529.AC90A9EF98@keescook/Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20231213-wmi_host_mem_chunks_flexarray-v1-1-92922d92fa2c@quicinc.com

drivers/net/wireless/ath/ath10k/wmi.h

@@ -3069,7 +3069,10 @@ struct host_memory_chunk {
 struct wmi_host_mem_chunks {
 	__le32 count;
 	/* some fw revisions require at least 1 chunk regardless of count */
-	struct host_memory_chunk items[1];
+	union {
+		struct host_memory_chunk item;
+		DECLARE_FLEX_ARRAY(struct host_memory_chunk, items);
+	};
 } __packed;
 
 struct wmi_init_cmd {