mac80211: reduce IEEE80211_TX_MAX_RATES

IEEE80211_TX_MAX_RATES can be reduced from 5 to 4 as there
is no current hardware supporting a rate chain with 5 multi
rate stages (mrr), so 4 mrr stages are sufficient.

The memory that is freed within the ieee80211_tx_info struct
will be used in the upcoming Transmission Power Control (TPC)
implementation.

Suggested-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
[reword commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/drivers/net/wireless/p54/txrx.c b/drivers/net/wireless/p54/txrx.c
index 82a1cac..f38786e 100644
--- a/drivers/net/wireless/p54/txrx.c
+++ b/drivers/net/wireless/p54/txrx.c
@@ -422,11 +422,11 @@
 	 * Clear manually, ieee80211_tx_info_clear_status would
 	 * clear the counts too and we need them.
 	 */
-	memset(&info->status.ampdu_ack_len, 0,
+	memset(&info->status.ack_signal, 0,
 	       sizeof(struct ieee80211_tx_info) -
-	       offsetof(struct ieee80211_tx_info, status.ampdu_ack_len));
+	       offsetof(struct ieee80211_tx_info, status.ack_signal));
 	BUILD_BUG_ON(offsetof(struct ieee80211_tx_info,
-			      status.ampdu_ack_len) != 23);
+			      status.ack_signal) != 20);
 
 	if (entry_hdr->flags & cpu_to_le16(P54_HDR_FLAG_DATA_ALIGN))
 		pad = entry_data->align[0];