snippet: Updated all snippet tags

Ensure all src C++ headers which have corresponding C++ examples have
doxygen tags which point to those examples.  Some were missing, some
were invalid, some needed to be updated to match the new example names.

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

src/mpu9150/ak8975.hpp

@@ -48,7 +48,7 @@ namespace upm {
    * coupled with another device (such as the mcu9150 9-axis motion
    * sensor).
    *
-   * @snippet ak8975.cxx Interesting
+   * @snippet mpu9150-ak8975.cxx Interesting
    */
   class AK8975 {
   public:

src/mpu9150/mpu60x0.hpp

@@ -57,7 +57,7 @@ namespace upm {
    * required.
    *
    * @image html mpu60x0.jpg
-   * @snippet mpu60x0.cxx Interesting
+   * @snippet mpu9150-mpu60x0.cxx Interesting
    */
   class MPU60X0 {
   public:

src/mpu9150/mpu9250.hpp

@@ -47,7 +47,7 @@ namespace upm {
    * This module defines the MPU9250 interface for libmpu9150
    *
    * @image html mpu9250.jpg
-   * @snippet mpu9250.cxx Interesting
+   * @snippet mpu9150-mpu9250.cxx Interesting
    */
 
   class MPU9250: public MPU9150