The `if let Some(gpio) = &self.gpio` causes a memory read of `self.gpio` for every Bus::read/write_16.
It is better to reverse the order since `is_gpio_access` does not generate and memory reads and thus less costly.
Former-commit-id: bcce7d9c3a2b159a7f6b291d7b08ccf9c4d0db14
Former-commit-id: 69c12db503c9e612faa7cd8a57f6d862694c8370
