ath9k_hw: replace magic values in register writes with proper defines

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.h b/drivers/net/wireless/ath/ath9k/ar9003_phy.h
index 59bab6b..8bdda2c 100644
--- a/drivers/net/wireless/ath/ath9k/ar9003_phy.h
+++ b/drivers/net/wireless/ath/ath9k/ar9003_phy.h
@@ -486,6 +486,8 @@
 #define AR_PHY_HEAVYCLIP_40      (AR_SM_BASE + 0x1ac)
 #define AR_PHY_ILLEGAL_TXRATE    (AR_SM_BASE + 0x1b0)
 
+#define AR_PHY_POWER_TX_RATE(_d) (AR_SM_BASE + 0x1c0 + ((_d) << 2))
+
 #define AR_PHY_PWRTX_MAX         (AR_SM_BASE + 0x1f0)
 #define AR_PHY_POWER_TX_SUB      (AR_SM_BASE + 0x1f4)