staging: wilc1000: adds a check routine when performed del_key()

This patch is adds a check routine when performed del_key().
We was find this situation while test the 'rmmod sdio'.
That is received inform a .del_key cmd from cfg80211.
If is not exist wep keys, must be ignore a wilc_remove_wep_key() function.
Thus, adds a check routine that key length of wep.
Signed-off-by: Leo Kim <leo.kim@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/wilc_wfi_cfgoperations.c

@@ -1122,9 +1122,12 @@ static int del_key(struct wiphy *wiphy, struct net_device *netdev,
 	}
 
 	if (key_index >= 0 && key_index <= 3) {
-		memset(priv->WILC_WFI_wep_key[key_index], 0, priv->WILC_WFI_wep_key_len[key_index]);
-		priv->WILC_WFI_wep_key_len[key_index] = 0;
-		wilc_remove_wep_key(vif, key_index);
+		if (priv->WILC_WFI_wep_key_len[key_index]) {
+			memset(priv->WILC_WFI_wep_key[key_index], 0,
+			       priv->WILC_WFI_wep_key_len[key_index]);
+			priv->WILC_WFI_wep_key_len[key_index] = 0;
+			wilc_remove_wep_key(vif, key_index);
+		}
 	} else {
 		wilc_remove_key(priv->hif_drv, mac_addr);
 	}