message: fix compilation on GCC <= 7.x
diff: @@ -89,6 +89,7 @@ bool Stm32SpiArbiter::transfer(SPI_InitTypeDef config, Stm32Gpio ncs_gpio, const
  .length = length,
  .on_complete = [](void* ctx, bool success) { *(volatile uint8_t*)ctx = success ? 1 : 0; },
  .on_complete_ctx = (void*)&result,
  + .is_in_use = false,
  .next = nullptr
  };
  