ath6kl: wmi: Replace one-element array with flexible-array member in struct wmi_aplist_event

Replace one-element array with flexible-array member in struct
wmi_aplist_event.

Also, make use of the struct_size() helper and remove unneeded variable
ap_info_entry_size.

This issue was found with the help of Coccinelle and audited and fixed,
manually.

Link: https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays
Link: https://github.com/KSPP/linux/issues/79Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/1b7889828f23763c034c1558cbab9c8e2066053e.1645736204.git.gustavoars@kernel.org

drivers/net/wireless/ath/ath6kl/wmi.c

@@ -1750,7 +1750,6 @@ static int ath6kl_wmi_snr_threshold_event_rx(struct wmi *wmi, u8 *datap,
 
 static int ath6kl_wmi_aplist_event_rx(struct wmi *wmi, u8 *datap, int len)
 {
-	u16 ap_info_entry_size;
 	struct wmi_aplist_event *ev = (struct wmi_aplist_event *) datap;
 	struct wmi_ap_info_v1 *ap_info_v1;
 	u8 index;
@@ -1759,14 +1758,12 @@ static int ath6kl_wmi_aplist_event_rx(struct wmi *wmi, u8 *datap, int len)
 	    ev->ap_list_ver != APLIST_VER1)
 		return -EINVAL;
 
-	ap_info_entry_size = sizeof(struct wmi_ap_info_v1);
 	ap_info_v1 = (struct wmi_ap_info_v1 *) ev->ap_list;
 
 	ath6kl_dbg(ATH6KL_DBG_WMI,
 		   "number of APs in aplist event: %d\n", ev->num_ap);
 
-	if (len < (int) (sizeof(struct wmi_aplist_event) +
-			 (ev->num_ap - 1) * ap_info_entry_size))
+	if (len < struct_size(ev, ap_list, ev->num_ap))
 		return -EINVAL;
 
 	/* AP list version 1 contents */

drivers/net/wireless/ath/ath6kl/wmi.h

@@ -1957,7 +1957,7 @@ union wmi_ap_info {
 struct wmi_aplist_event {
 	u8 ap_list_ver;
 	u8 num_ap;
-	union wmi_ap_info ap_list[1];
+	union wmi_ap_info ap_list[];
 } __packed;
 
 /* Developer Commands */