ASoC: mediatek: btcvsd fix tx stream assign

Fix tx/rx stream assign in write.
Write should use tx instead of rx.
Signed-off-by: Lumi Lee <lumi.lee@mediatek.com>
Link: https://lore.kernel.org/r/1606705875-1940-1-git-send-email-Lumi.Lee@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/mediatek/common/mtk-btcvsd.c

@@ -808,7 +808,7 @@ static ssize_t mtk_btcvsd_snd_write(struct mtk_btcvsd_snd *bt,
 		spin_unlock_irqrestore(&bt->tx_lock, flags);
 
 		if (!avail) {
-			int ret = wait_for_bt_irq(bt, bt->rx);
+			int ret = wait_for_bt_irq(bt, bt->tx);
 
 			if (ret)
 				return written_size;