mac80211: remove the need for variable rates_idx

Currently rates_idx is being initialized with the value -1 and this
value is never read so the initialization is redundant and can be
removed. The next time the variable is used it is assigned a value
that is returned a few statements later. Just return i - 1 and
remove the need for rates_idx.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20200722153830.959010-1-colin.king@canonical.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/status.c

@@ -799,7 +799,6 @@ static int ieee80211_tx_get_rates(struct ieee80211_hw *hw,
 				  struct ieee80211_tx_info *info,
 				  int *retry_count)
 {
-	int rates_idx = -1;
 	int count = -1;
 	int i;
 
@@ -821,13 +820,12 @@ static int ieee80211_tx_get_rates(struct ieee80211_hw *hw,
 
 		count += info->status.rates[i].count;
 	}
-	rates_idx = i - 1;
 
 	if (count < 0)
 		count = 0;
 
 	*retry_count = count;
-	return rates_idx;
+	return i - 1;
 }
 
 void ieee80211_tx_monitor(struct ieee80211_local *local, struct sk_buff *skb,