ath9k_htc: fix random decryption failure

In v3.15 the driver stopped to accept network packets after successful
authentification, which could be worked around by passing the
nohwcrypt=1 module parameter.  This was not reproducible by
everyone, and showed random behaviour in some tests.
It was caused by an uninitialized variable introduced
in 4ed1a8d4a257 ("ath9k_htc: use ath9k_cmn_rx_accept") and
used in 341b29b9cd2f ("ath9k_htc: use ath9k_cmn_rx_skb_postprocess").

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=78581
Fixes: 341b29b9cd2f ("ath9k_htc: use ath9k_cmn_rx_skb_postprocess")
Signed-off-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -978,7 +978,7 @@ static bool ath9k_rx_prepare(struct ath9k_htc_priv *priv,
 	struct ath_hw *ah = common->ah;
 	struct ath_htc_rx_status *rxstatus;
 	struct ath_rx_status rx_stats;
-	bool decrypt_error;
+	bool decrypt_error = false;
 
 	if (skb->len < HTC_RX_FRAME_HEADER_SIZE) {
 		ath_err(common, "Corrupted RX frame, dropping (len: %d)\n",