zd1211rw: fix potential array underflow

The first chunk fixes a debugging assert to print a warning about array underflows.
The second chunk corrects a potential array underflow.  I also removed an assert
in the second chunk because it can no longer happen.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/zd1211rw/zd_mac.c

@@ -350,7 +350,7 @@ static void zd_mac_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
 	first_idx = info->status.rates[0].idx;
 	ZD_ASSERT(0<=first_idx && first_idx<ARRAY_SIZE(zd_retry_rates));
 	retries = &zd_retry_rates[first_idx];
-	ZD_ASSERT(0<=retry && retry<=retries->count);
+	ZD_ASSERT(1 <= retry && retry <= retries->count);
 
 	info->status.rates[0].idx = retries->rate[0];
 	info->status.rates[0].count = 1; // (retry > 1 ? 2 : 1);
@@ -360,7 +360,7 @@ static void zd_mac_tx_status(struct ieee80211_hw *hw, struct sk_buff *skb,
 		info->status.rates[i].count = 1; // ((i==retry-1) && success ? 1:2);
 	}
 	for (; i<IEEE80211_TX_MAX_RATES && i<retry; i++) {
-		info->status.rates[i].idx = retries->rate[retry-1];
+		info->status.rates[i].idx = retries->rate[retry - 1];
 		info->status.rates[i].count = 1; // (success ? 1:2);
 	}
 	if (i<IEEE80211_TX_MAX_RATES)
@@ -424,12 +424,10 @@ void zd_mac_tx_failed(struct urb *urb)
 		first_idx = info->status.rates[0].idx;
 		ZD_ASSERT(0<=first_idx && first_idx<ARRAY_SIZE(zd_retry_rates));
 		retries = &zd_retry_rates[first_idx];
-		if (retry < 0 || retry > retries->count) {
+		if (retry <= 0 || retry > retries->count)
 			continue;
-		}
 
-		ZD_ASSERT(0<=retry && retry<=retries->count);
-		final_idx = retries->rate[retry-1];
+		final_idx = retries->rate[retry - 1];
 		final_rate = zd_rates[final_idx].hw_value;
 
 		if (final_rate != tx_status->rate) {