soc: mediatek: cmdq: return send msg error code

Return error code to client if send message fail,
so that client has chance to error handling.

Fixes: 576f1b4 ("soc: mediatek: Add Mediatek CMDQ helper")
Signed-off-by: Dennis YC Hsieh <dennis-yc.hsieh@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://lore.kernel.org/r/1583664775-19382-6-git-send-email-dennis-yc.hsieh@mediatek.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>

drivers/soc/mediatek/mtk-cmdq-helper.c

@@ -351,7 +351,9 @@ int cmdq_pkt_flush_async(struct cmdq_pkt *pkt, cmdq_async_flush_cb cb,
 		spin_unlock_irqrestore(&client->lock, flags);
 	}
 
-	mbox_send_message(client->chan, pkt);
+	err = mbox_send_message(client->chan, pkt);
+	if (err < 0)
+		return err;
 	/* We can send next packet immediately, so just call txdone. */
 	mbox_client_txdone(client->chan, 0);