ath9k: Remove redundant NULL assignment

'bf_next' is cleared using ATH_TXBUF_RESET() in both the
callsites of ath_tx_get_buffer().
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -312,7 +312,6 @@ static struct ath_buf *ath_tx_get_buffer(struct ath_softc *sc)
 	}
 
 	bf = list_first_entry(&sc->tx.txbuf, struct ath_buf, list);
-	bf->bf_next = NULL;
 	list_del(&bf->list);
 
 	spin_unlock_bh(&sc->tx.txbuflock);