rtc: hym8563: make the irq optional

Sometimes the irq line is not connected to any soc-pin. This does
not hinder basic timekeeping functionality of the rtc, so probe
should not fail in this case.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/rtc-hym8563.c b/drivers/rtc/rtc-hym8563.c
index 0f710e9..e9da795 100644
--- a/drivers/rtc/rtc-hym8563.c
+++ b/drivers/rtc/rtc-hym8563.c
@@ -548,14 +548,16 @@
 		return ret;
 	}
 
-	ret = devm_request_threaded_irq(&client->dev, client->irq,
-					NULL, hym8563_irq,
-					IRQF_TRIGGER_LOW | IRQF_ONESHOT,
-					client->name, hym8563);
-	if (ret < 0) {
-		dev_err(&client->dev, "irq %d request failed, %d\n",
-			client->irq, ret);
-		return ret;
+	if (client->irq > 0) {
+		ret = devm_request_threaded_irq(&client->dev, client->irq,
+						NULL, hym8563_irq,
+						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+						client->name, hym8563);
+		if (ret < 0) {
+			dev_err(&client->dev, "irq %d request failed, %d\n",
+				client->irq, ret);
+			return ret;
+		}
 	}
 
 	/* check state of calendar information */