libpixelflinger: Fix -Woverloaded-virtual warnings.

private:

    // GGLAssembler hides RegisterAllocator's and ARMAssemblerProxy's reset

    // methods by providing a reset method with a different parameter set. The

    // intent of GGLAssembler's reset method is to wrap the inherited reset

    // methods, so make these methods private in order to prevent direct calls

    // to these methods from clients.

    using RegisterAllocator::reset;

    using ARMAssemblerProxy::reset;

    struct tex_coord_t {

        reg_t       s;

        reg_t       t;