iwlwifi: fix HT operation in 2.4 GHz band

When we cleaned up the driver to properly tell mac80211 about HT rates
("iwlwifi: use iwl_hwrate_get_mac80211_idx where appropriate"), we broke
internal rate indexing in 2.4 GHz band.
Signed-off-by: Daniel C Halperin <daniel.c.halperin@intel.com>
Tested-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-agn-rs.c

@@ -883,6 +883,12 @@ static void rs_tx_status(void *priv_r, struct ieee80211_supported_band *sband,
 		mac_index &= RATE_MCS_CODE_MSK;	/* Remove # of streams */
 		if (mac_index >= (IWL_RATE_9M_INDEX - IWL_FIRST_OFDM_RATE))
 			mac_index++;
+		/*
+		 * mac80211 HT index is always zero-indexed; we need to move
+		 * HT OFDM rates after CCK rates in 2.4 GHz band
+		 */
+		if (priv->band == IEEE80211_BAND_2GHZ)
+			mac_index += IWL_FIRST_OFDM_RATE;
 	}
 
 	if ((mac_index < 0) ||