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>

Documentation/devicetree/bindings/rtc/haoyu,hym8563.txt

@@ -6,11 +6,11 @@ as well as a clock output of up to 32kHz.
 Required properties:
 - compatible: should be: "haoyu,hym8563"
 - reg: i2c address
-- interrupts: rtc alarm/event interrupt
 - #clock-cells: the value should be 0
 
 Optional properties:
 - clock-output-names: From common clock binding
+- interrupts: rtc alarm/event interrupt
 
 Example:
 

drivers/rtc/rtc-hym8563.c

@@ -548,6 +548,7 @@ static int hym8563_probe(struct i2c_client *client,
 		return ret;
 	}
 
+	if (client->irq > 0) {
 		ret = devm_request_threaded_irq(&client->dev, client->irq,
 						NULL, hym8563_irq,
 						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
@@ -557,6 +558,7 @@ static int hym8563_probe(struct i2c_client *client,
 				client->irq, ret);
 			return ret;
 		}
+	}
 
 	/* check state of calendar information */
 	ret = i2c_smbus_read_byte_data(client, HYM8563_SEC);