ath9k_hw: add OFDM spur mitigation for AR9003

We add this now as OFDM spur mitigation required accessing
the EEPROM for the AR9003 devices.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index d1b9940..25713be 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -76,6 +76,8 @@
 #define REG_RMW_FIELD(_a, _r, _f, _v) \
 	REG_WRITE(_a, _r, \
 	(REG_READ(_a, _r) & ~_f) | (((_v) << _f##_S) & _f))
+#define REG_READ_FIELD(_a, _r, _f) \
+	(((REG_READ(_a, _r) & _f) >> _f##_S))
 #define REG_SET_BIT(_a, _r, _f) \
 	REG_WRITE(_a, _r, REG_READ(_a, _r) | _f)
 #define REG_CLR_BIT(_a, _r, _f) \