ath9k_hw: fix spur mitigation issues on AR934x

Do not subtract spur power from noise floor on this chip, as it can lead
to packet loss and other connectivity issues.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/ar9003_phy.c b/drivers/net/wireless/ath/ath9k/ar9003_phy.c
index 2bf6548..e1714d7 100644
--- a/drivers/net/wireless/ath/ath9k/ar9003_phy.c
+++ b/drivers/net/wireless/ath/ath9k/ar9003_phy.c
@@ -334,7 +334,8 @@
 	REG_RMW_FIELD(ah, AR_PHY_SPUR_REG,
 		      AR_PHY_SPUR_REG_EN_VIT_SPUR_RSSI, 1);
 
-	if (REG_READ_FIELD(ah, AR_PHY_MODE,
+	if (!AR_SREV_9340(ah) &&
+	    REG_READ_FIELD(ah, AR_PHY_MODE,
 			   AR_PHY_MODE_DYNAMIC) == 0x1)
 		REG_RMW_FIELD(ah, AR_PHY_SPUR_REG,
 			      AR_PHY_SPUR_REG_ENABLE_NF_RSSI_SPUR_MIT, 1);