iwmc3200wifi: add a range check to iwm_cfg80211_get_key()

Smatch complains that "key_index" is capped at 5 in nl80211_get_key()
but iwm->keys[] only has 4 elements.  I don't know if this is really
needed, but the other ->get_key() implementations seemed to check
for overflows so I've added a check here.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwmc3200wifi/cfg80211.c

@@ -187,13 +187,17 @@ static int iwm_cfg80211_get_key(struct wiphy *wiphy, struct net_device *ndev,
 						 struct key_params*))
 {
 	struct iwm_priv *iwm = ndev_to_iwm(ndev);
-	struct iwm_key *key = &iwm->keys[key_index];
+	struct iwm_key *key;
 	struct key_params params;
 
 	IWM_DBG_WEXT(iwm, DBG, "Getting key %d\n", key_index);
 
+	if (key_index >= IWM_NUM_KEYS)
+		return -ENOENT;
+
 	memset(&params, 0, sizeof(params));
 
+	key = &iwm->keys[key_index];
 	params.cipher = key->cipher;
 	params.key_len = key->key_len;
 	params.seq_len = key->seq_len;