message: [MICRO] Fix for custom operator
  Changed micro_mtable_op_resolver.cc
  to use BuiltinOperator_CUSTOM.
diff: @@ -33,7 +33,7 @@ const TfLiteRegistration* MicroMutableOpResolver::FindOp(const char* op,
  int version) const {
  for (int i = 0; i < registrations_len_; ++i) {
  const TfLiteRegistration& registration = registrations_[i];
  - if ((registration.builtin_code == -1) &&
  + if ((registration.builtin_code == BuiltinOperator_CUSTOM) &&
  (strcmp(registration.custom_name, op) == 0) &&
  (registration.version == version)) {
  return &registration;
  @@ -71,7 +71,7 @@ void MicroMutableOpResolver::AddCustom(const char* name,
  registrations_len_ += 1;
  *new_registration = *registration;
  - new_registration->builtin_code = -1;
  + new_registration->builtin_code = BuiltinOperator_CUSTOM;
  new_registration->custom_name = name;
  new_registration->version = version;
  }
  