ath9k: Don't read NF when chip has gone through full sleep mode

NF value may be incorrect when we read it just after the chip
has gone through a full sleep mode. Reading incorrect NF values
affects RX throughput.
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hw.c

@@ -2357,7 +2357,7 @@ int ath9k_hw_reset(struct ath_hw *ah, struct ath9k_channel *chan,
 	if (!ath9k_hw_setpower(ah, ATH9K_PM_AWAKE))
 		return -EIO;
 
-	if (curchan)
+	if (curchan && !ah->chip_fullsleep)
 		ath9k_hw_getnf(ah, curchan);
 
 	if (bChannelChange &&