Wnon-virtual-dtor: Fixed all virtual functions w/o virtual destructor

This commit addresses all warnings emitted from -Wnon-virtual-dtor
in the C++ src.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/my9221/grovecircularled.hpp

@@ -72,7 +72,7 @@ namespace upm {
     /**
      * GroveCircularLED destructor
      */
-    ~GroveCircularLED();
+    virtual ~GroveCircularLED();
 
     /**
      * Sets the spinner (turns off all LEDs but selected one)

src/my9221/groveledbar.hpp

@@ -78,7 +78,7 @@ namespace upm {
     /**
      * GroveLEDBar destructor
      */
-    ~GroveLEDBar();
+    virtual ~GroveLEDBar();
 
     /**
      * Sets the bar level

src/my9221/my9221.hpp

@@ -63,7 +63,7 @@ namespace upm {
     /**
      * MY9221 destructor
      */
-    ~MY9221();
+    virtual ~MY9221();
 
     /**
      * Enable or disable auto refresh.  When auto refresh is enabled,