mac80211: Remove unused 'rates_idx' variable

Commit f027c2aca0cf introduced 'rates_idx' in
ieee80211_tx_status_noskb but did not use it. Compiling with W=1
gives the following warning, fix it.

mac80211/status.c: In function ‘ieee80211_tx_status_noskb’:
mac80211/status.c:636:6: warning: variable ‘rates_idx’ set but not used [-Wunused-but-set-variable]

This is a harmless warning, and is only being fixed to reduce the
noise generated with W=1.

Fixes: f027c2aca0cf ("mac80211: add ieee80211_tx_status_noskb")
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Kirtika Ruchandani <kirtika@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/status.c

@@ -633,10 +633,9 @@ void ieee80211_tx_status_noskb(struct ieee80211_hw *hw,
 	struct ieee80211_local *local = hw_to_local(hw);
 	struct ieee80211_supported_band *sband;
 	int retry_count;
-	int rates_idx;
 	bool acked, noack_success;
 
-	rates_idx = ieee80211_tx_get_rates(hw, info, &retry_count);
+	ieee80211_tx_get_rates(hw, info, &retry_count);
 
 	sband = hw->wiphy->bands[info->band];