maiblox: mediatek: Fix handling of platform_get_irq() error

platform_get_irq() returns -ERRNO on error. In such case casting to u32
and comparing to 0 would pass the check.

Fixes: 623a6143a845 ("mailbox: mediatek: Add Mediatek CMDQ driver")
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

drivers/mailbox/mtk-cmdq-mailbox.c

···
 struct cmdq {
 	struct mbox_controller	mbox;
 	void __iomem		*base;
-	u32			irq;
+	int			irq;
 	u32			thread_nr;
 	u32			irq_mask;
 	struct cmdq_thread	*thread;
···
 	}
 
 	cmdq->irq = platform_get_irq(pdev, 0);
-	if (!cmdq->irq) {
-		dev_err(dev, "failed to get irq\n");
-		return -EINVAL;
-	}
+	if (cmdq->irq < 0)
+		return cmdq->irq;
 
 	plat_data = (struct gce_plat *)of_device_get_match_data(dev);
 	if (!plat_data) {