Define Sensor::readingStateGood() in terms of readingStateGood()

We can reuse the same logic instead of duplicating it between the
generic global function and the Sensor class method.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Change-Id: Ibc77c2fe538398a013aab2b13964e37bb6f17f9e
diff --git a/include/sensor.hpp b/include/sensor.hpp
index 4578935..f278212 100644
--- a/include/sensor.hpp
+++ b/include/sensor.hpp
@@ -423,20 +423,7 @@
 
     bool readingStateGood() const
     {
-        if (readState == PowerState::on && !isPowerOn())
-        {
-            return false;
-        }
-        if (readState == PowerState::biosPost &&
-            (!hasBiosPost() || !isPowerOn()))
-        {
-            return false;
-        }
-        if (readState == PowerState::chassisOn && !isChassisOn())
-        {
-            return false;
-        }
-        return true;
+        return ::readingStateGood(readState);
     }
 
     void markFunctional(bool isFunctional)