iio:magnetometer:hmc5843 - add basic dt support

Compatible string, documenation and an optional gpio
for the dataready pin.

Signed-off-by: NeilBrown <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/magnetometer/hmc5843.txt

···
+* Honeywell HMC5843 magnetometer sensor
+
+Required properties:
+
+  - compatible : should be "honeywell,hmc5843"
+  - reg : the I2C address of the magnetometer - typically 0x1e
+
+Optional properties:
+
+  - gpios : should be device tree identifier of the magnetometer DRDY pin
+
+Example:
+
+hmc5843@1e {
+        compatible = "honeywell,hmc5843"
+        reg = <0x1e>;
+};

drivers/staging/iio/magnetometer/hmc5843.c

···
 };
 MODULE_DEVICE_TABLE(i2c, hmc5843_id);
 
+static const struct of_device_id hmc5843_of_match[] = {
+	{ .compatible = "honeywell,hmc5843" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, hmc5843_of_match);
+
 static struct i2c_driver hmc5843_driver = {
 	.driver = {
 		.name	= "hmc5843",
 		.pm	= HMC5843_PM_OPS,
+		.of_match_table = of_match_ptr(hmc5843_of_match),
 	},
 	.id_table	= hmc5843_id,
 	.probe		= hmc5843_probe,