libertas_tf: remove usage of deprecated noise value

Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas_tf/main.c

@@ -555,7 +555,6 @@ int lbtf_rx(struct lbtf_private *priv, struct sk_buff *skb)
 	stats.freq = priv->cur_freq;
 	stats.band = IEEE80211_BAND_2GHZ;
 	stats.signal = prxpd->snr;
-	stats.noise = prxpd->nf;
 	/* Marvell rate index has a hole at value 4 */
 	if (prxpd->rx_rate > 4)
 		--prxpd->rx_rate;