wilc1000: use flexible-array member instead of zero-length array

Use flexible-array member introduced in C99 instead of zero-length
array. Most of zero-length array was already taken care in previous
patch [1].

[1]. https://patchwork.kernel.org/patch/11394197/Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1608881703-37060-1-git-send-email-tiantao6@hisilicon.com

drivers/net/wireless/microchip/wilc1000/fw.h

@@ -44,20 +44,20 @@ struct wilc_drv_handler {
 struct wilc_wep_key {
 	u8 index;
 	u8 key_len;
-	u8 key[0];
+	u8 key[];
 } __packed;
 
 struct wilc_sta_wpa_ptk {
 	u8 mac_addr[ETH_ALEN];
 	u8 key_len;
-	u8 key[0];
+	u8 key[];
 } __packed;
 
 struct wilc_ap_wpa_ptk {
 	u8 mac_addr[ETH_ALEN];
 	u8 index;
 	u8 key_len;
-	u8 key[0];
+	u8 key[];
 } __packed;
 
 struct wilc_gtk_key {
@@ -65,7 +65,7 @@ struct wilc_gtk_key {
 	u8 rsc[8];
 	u8 index;
 	u8 key_len;
-	u8 key[0];
+	u8 key[];
 } __packed;
 
 struct wilc_op_mode {