ath9k_hw: Add function to configure tx status ring buffer

Also reset tx status ring suring chip reset.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index 824dd9e..19e2c3c 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -895,6 +895,9 @@
 		REG_WRITE(ah, AR_PCU_TXBUF_CTRL,
 			  AR_PCU_TXBUF_CTRL_USABLE_SIZE);
 	}
+
+	if (AR_SREV_9300_20_OR_LATER(ah))
+		ath9k_hw_reset_txstatus_ring(ah);
 }
 
 static void ath9k_hw_set_operating_mode(struct ath_hw *ah, int opmode)