ath9k: fix a crash in the PA predistortion apply function

When updating the PAPRD table in hardware, PAPRD itself needs to be
disabled first, otherwise the hardware can throw a data bus error,
which upsets at least some platforms.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -239,6 +239,7 @@ static void ath_paprd_activate(struct ath_softc *sc)
 		return;
 
 	ath9k_ps_wakeup(sc);
+	ar9003_paprd_enable(ah, false);
 	for (chain = 0; chain < AR9300_MAX_CHAINS; chain++) {
 		if (!(ah->caps.tx_chainmask & BIT(chain)))
 			continue;