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: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 35b515f..a749e0f 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -399,6 +399,7 @@
 	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;
 }