ath9k_hw: remove dead code in the eeprom ops

The eeprom .set_addac function is only necessary for AR9160, remove it
from eeprom_4k.c and remove the dummy function from eeprom_9287.c

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/ar5008_phy.c b/drivers/net/wireless/ath/ath9k/ar5008_phy.c
index b130c26..1381a39 100644
--- a/drivers/net/wireless/ath/ath9k/ar5008_phy.c
+++ b/drivers/net/wireless/ath/ath9k/ar5008_phy.c
@@ -801,7 +801,8 @@
 
 	/* Write ADDAC shifts */
 	REG_WRITE(ah, AR_PHY_ADC_SERIAL_CTL, AR_PHY_SEL_EXTERNAL_RADIO);
-	ah->eep_ops->set_addac(ah, chan);
+	if (ah->eep_ops->set_addac)
+		ah->eep_ops->set_addac(ah, chan);
 
 	if (AR_SREV_5416_22_OR_LATER(ah)) {
 		REG_WRITE_ARRAY(&ah->iniAddac, 1, regWrites);