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/mpu9150/mpu60x0.hpp

@@ -661,8 +661,8 @@ namespace upm {
     /**
      * MPU60X0 Destructor
      */
-    ~MPU60X0();
-    
+    virtual ~MPU60X0();
+
     /**
      * set up initial values and start operation
      *

src/mpu9150/mpu9150.hpp

@@ -75,7 +75,7 @@ namespace upm {
     /**
      * MPU9150 destructor
      */
-    ~MPU9150 ();
+    virtual ~MPU9150 ();
 
     /**
      * Set up initial values and start operation