Fix Field member function to avoid back storage warning message when using CUDA

The GetStorage function should not be called internally in the Field class member function because the MemoryRegion template parameter can't be properly specified for the Field input parameter. The problem appears for the following function:

    bool compare(Field<TData, TState> &rhs, TData tol)

    void CopyDataFrom(Field<TData, TState> &rhs, size_t rhs_component = 0,
                      size_t component = 0)
    {