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

Replace one-element array with flexible-array member in struct
wmi_begin_scan_cmd. Also, make use of the struct_size() helper.

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/1ef801ea24475501fa0f296cb5435a440135206e.1645736204.git.gustavoars@kernel.org

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

@@ -2008,7 +2008,7 @@ int ath6kl_wmi_beginscan_cmd(struct wmi *wmi, u8 if_idx,
 	struct ieee80211_supported_band *sband;
 	struct sk_buff *skb;
 	struct wmi_begin_scan_cmd *sc;
-	s8 size, *supp_rates;
+	s8 *supp_rates;
 	int i, band, ret;
 	struct ath6kl *ar = wmi->parent_dev;
 	int num_rates;
@@ -2023,18 +2023,13 @@ int ath6kl_wmi_beginscan_cmd(struct wmi *wmi, u8 if_idx,
 						num_chan, ch_list);
 	}
 
-	size = sizeof(struct wmi_begin_scan_cmd);
-
 	if ((scan_type != WMI_LONG_SCAN) && (scan_type != WMI_SHORT_SCAN))
 		return -EINVAL;
 
 	if (num_chan > WMI_MAX_CHANNELS)
 		return -EINVAL;
 
-	if (num_chan)
-		size += sizeof(u16) * (num_chan - 1);
-
-	skb = ath6kl_wmi_get_new_buf(size);
+	skb = ath6kl_wmi_get_new_buf(struct_size(sc, ch_list, num_chan));
 	if (!skb)
 		return -ENOMEM;
 

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

@@ -863,7 +863,7 @@ struct wmi_begin_scan_cmd {
 	u8 num_ch;
 
 	/* channels in Mhz */
-	__le16 ch_list[1];
+	__le16 ch_list[];
 } __packed;
 
 /* wmi_start_scan_cmd is to be deprecated. Use