occ-sensor: clean dt properties if sensor is not available

In `occ_sensor_init()` device tree node is created for sensor-goups
and performs `occ_sensor_sanity()` check to initialize the device
tree. But if there are no sensors like in Qemu, sanity check fails
but still device tree populates the sensor-groups node wrongly as
the node created is not cleaned up.

Signed-off-by: Balamuruhan S <bala24@linux.ibm.com>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

hw/occ-sensor.c

@@ -587,6 +587,10 @@ bool occ_sensors_init(void)
 		free(phandles);
 		free(ptype);
 	}
+	/* clear the device tree property if no sensors */
+	if (list_empty(&sg->children)) {
+               dt_free(sg);
+	}
 
 	if (!occ_num)
 		return false;