staging: vt6656: vnt_get_rtscts_duration_le use ieee80211_rts_duration

use the mac80211 ieee80211_rts_duration for RTS frames.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Link: https://lore.kernel.org/r/377a4cc3-cfe3-91aa-cf71-1063f311426a@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/rxtx.c

@@ -280,28 +280,18 @@ static __le16 vnt_get_rtscts_duration_le(struct vnt_usb_send_context *context,
 					 u8 dur_type, u8 pkt_type, u16 rate)
 {
 	struct vnt_private *priv = context->priv;
-	u32 cts_time = 0, dur_time = 0;
+	u32 dur_time = 0;
 	u32 frame_length = context->frame_len;
 	u8 need_ack = context->need_ack;
+	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(context->skb);
 
 	switch (dur_type) {
+	/* fall through */
 	case RTSDUR_BB:
 	case RTSDUR_BA:
-		cts_time = vnt_get_frame_time(priv->preamble_type, pkt_type,
-					      14, priv->top_cck_basic_rate);
-		dur_time = cts_time + 2 * priv->sifs +
-			vnt_get_rsvtime(priv, pkt_type,
-					frame_length, rate, need_ack);
-		break;
-
 	case RTSDUR_AA:
-		cts_time = vnt_get_frame_time(priv->preamble_type, pkt_type,
-					      14, priv->top_ofdm_basic_rate);
-		dur_time = cts_time + 2 * priv->sifs +
-			vnt_get_rsvtime(priv, pkt_type,
-					frame_length, rate, need_ack);
-		break;
-
+		return ieee80211_rts_duration(priv->hw, priv->vif,
+					      context->frame_len, info);
 	case CTSDUR_BA:
 		dur_time = priv->sifs + vnt_get_rsvtime(priv,
 				pkt_type, frame_length, rate, need_ack);