mailbox: mtk-cmdq: Fix pm_runtime_get_sync() warning in mbox shutdown

The return value of pm_runtime_get_sync() in cmdq_mbox_shutdown()
will return 1 when pm runtime state is active, and we don't want to
get the warning message in this case.

So we change the return value < 0 for WARN_ON().

Fixes: 8afe816b ("mailbox: mtk-cmdq-mailbox: Implement Runtime PM with autosuspend")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

drivers/mailbox/mtk-cmdq-mailbox.c

@@ -465,7 +465,7 @@ static void cmdq_mbox_shutdown(struct mbox_chan *chan)
 	struct cmdq_task *task, *tmp;
 	unsigned long flags;
 
-	WARN_ON(pm_runtime_get_sync(cmdq->mbox.dev));
+	WARN_ON(pm_runtime_get_sync(cmdq->mbox.dev) < 0);
 
 	spin_lock_irqsave(&thread->chan->lock, flags);
 	if (list_empty(&thread->task_busy_list))