Ok... if I change the files gl2.h, gl2ext.h and gl2platform.h (from OGRE/RenderSystems/GLES2) for the ones that come with Android-NDK the error disappears.
Then you should use the Qt resource system to embed the shader in your application. You current shader files are accessible on your host. When you start your application on your device, they won't be there.
Follow thoose tutorials or at least the part 0, 1 ,2 ,3a, 3b and you will have decent basis to start.
In the tutorial he use QOpenGLWindow which isn't really far from QOpenGLWidget so I think you should be able to adapt his code a bit to suit your need but if you didn't succed to do it ask here again.