pwmsensor: Correct the type of MaxValue/MinValue

The MaxValue/MinValue must be double so that redfish can read the value

Before:
{
  "@odata.id": "/redfish/v1/Chassis/<chassis>/Thermal#/Fans/0",
  "@odata.type": "#Thermal.v1_3_0.Fan",
  "MemberId": "fan0_pwm",
  "Name": "fan0 pwm",
  "Reading": 25,
  "ReadingUnits": "Percent",
  "Status": {
    "Health": "OK",
    "State": "Enabled"
  }
},

After:
{
  "@odata.id": "/redfish/v1/Chassis/<chassis>/Thermal#/Fans/0",
  "@odata.type": "#Thermal.v1_3_0.Fan",
  "MaxReadingRange": 100,
  "MemberId": "fan0_pwm",
  "MinReadingRange": 0,
  "Name": "fan0 pwm",
  "Reading": 90,
  "ReadingUnits": "Percent",
  "Status": {
    "Health": "OK",
    "State": "Enabled"
  }
},

ref:
https://github.com/openbmc/phosphor-dbus-interfaces/blob/a134741830/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml#L27-L36

Signed-off-by: David Wang <davidwang@quantatw.com>
Change-Id: I2e1c94648d344988f23aef68fe7a70ad0d7ba3b8
diff --git a/src/PwmSensor.cpp b/src/PwmSensor.cpp
index ae7b240..0ee8c88 100644
--- a/src/PwmSensor.cpp
+++ b/src/PwmSensor.cpp
@@ -104,8 +104,8 @@
         return curVal;
     });
     // pwm sensor interface is in percent
-    sensorInterface->register_property("MaxValue", static_cast<int64_t>(100));
-    sensorInterface->register_property("MinValue", static_cast<int64_t>(0));
+    sensorInterface->register_property("MaxValue", static_cast<double>(100));
+    sensorInterface->register_property("MinValue", static_cast<double>(0));
     sensorInterface->register_property("Unit", sensor_paths::unitPercent);
 
     controlInterface = objectServer.add_interface(