sensors: host: Implement getFailed function to HostSensor

1. Add getFailed function to check the dbus value in HostSensor
   is finite or not, if not, pid control will into failsafe mode.

Signed-off-by: Harvey Wu <Harvey.Wu@quantatw.com>
Change-Id: Ib198aecf512a3a107793319014f6c0b531cc6211
diff --git a/sensors/host.hpp b/sensors/host.hpp
index 35c7f45..5c70526 100644
--- a/sensors/host.hpp
+++ b/sensors/host.hpp
@@ -55,6 +55,7 @@
 
     ReadReturn read(void) override;
     void write(double value) override;
+    bool getFailed(void) override;
 
   private:
     /*