monitor: Tach input to double

It was found that after the Value property on the Sensor.Value interface
was changed to be of double type, the tach input failed to get converted
correctly from double to int64 type when the property changed. Need to
set the tach input to be of double type explicitly.

Tested:
    Tach input values correctly read from dbus signal

Change-Id: I718375d5de50a88bcfaf8ff419e71f732d0b8a65
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/monitor/tach_sensor.hpp b/monitor/tach_sensor.hpp
index 7ad3c79..27e0626 100644
--- a/monitor/tach_sensor.hpp
+++ b/monitor/tach_sensor.hpp
@@ -94,7 +94,7 @@
     /**
      * @brief Returns the input speed value
      */
-    inline int64_t getInput() const
+    inline double getInput() const
     {
         return _tachInput;
     }
@@ -274,7 +274,7 @@
     /**
      * @brief The input speed, from the Value dbus property
      */
-    int64_t _tachInput = 0;
+    double _tachInput = 0;
 
     /**
      * @brief The current target speed, from the Target dbus property