ath9k: fix stale flag handling on buffer clone

Fixes a regression from commit
"ath9k: shrink a few data structures by reordering fields"

When cloning a buffer, the stale flag (part of bf_state now) needs to be
reset after copying the state to prevent tx processing hangs.
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -399,6 +399,7 @@ static struct ath_buf* ath_clone_txbuf(struct ath_softc *sc, struct ath_buf *bf)
 	tbf->bf_buf_addr = bf->bf_buf_addr;
 	memcpy(tbf->bf_desc, bf->bf_desc, sc->sc_ah->caps.tx_desc_len);
 	tbf->bf_state = bf->bf_state;
+	tbf->bf_state.stale = false;
 
 	return tbf;
 }