ath9k: Fix bugs in handling TX power

* Get power table offset from the EEPROM instead of using
  a hardcoded value of -5 if the EEPROM rev is >= 21.
* Add support in the 4k eeprom code for tx power offset
  in case we have a 4k AR9280 implementation.
* Fix tx power accuracy at high powers.

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/eeprom.h b/drivers/net/wireless/ath/ath9k/eeprom.h
index 3349274..2f2993b 100644
--- a/drivers/net/wireless/ath/ath9k/eeprom.h
+++ b/drivers/net/wireless/ath/ath9k/eeprom.h
@@ -134,6 +134,7 @@
 #define AR5416_EEP_MINOR_VER_17      0x11
 #define AR5416_EEP_MINOR_VER_19      0x13
 #define AR5416_EEP_MINOR_VER_20      0x14
+#define AR5416_EEP_MINOR_VER_21      0x15
 #define AR5416_EEP_MINOR_VER_22      0x16
 
 #define AR5416_NUM_5G_CAL_PIERS         8
@@ -154,7 +155,7 @@
 #define AR5416_BCHAN_UNUSED             0xFF
 #define AR5416_MAX_PWR_RANGE_IN_HALF_DB 64
 #define AR5416_MAX_CHAINS               3
-#define AR5416_PWR_TABLE_OFFSET         -5
+#define AR5416_PWR_TABLE_OFFSET_DB     -5
 
 /* Rx gain type values */
 #define AR5416_EEP_RXGAIN_23DB_BACKOFF     0
@@ -302,7 +303,7 @@
 	u8 txGainType;
 	u8 rcChainMask;
 	u8 desiredScaleCCK;
-	u8 power_table_offset;
+	u8 pwr_table_offset;
 	u8 frac_n_5g;
 	u8 futureBase_3[21];
 } __packed;