ath9k: fix PA linearization calibration related crash

Before PAPRD training can run, the card needs to have sent a packet for
thermal calibration. Sending a dummy packet with the PAPRD training flag
set causes a crash under some circumstance.
Fix the code by replacing the dummy tx with a delay that waits for a
real packet tx to have occurred.

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/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index ce7332c..6599a75 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -405,6 +405,7 @@
 	int8_t iCoff;
 	int8_t qCoff;
 	bool rtt_done;
+	bool paprd_packet_sent;
 	bool paprd_done;
 	bool nfcal_pending;
 	bool nfcal_interference;