Program panics when accessing the SPI device

[f-bro]

Hi,

I want to change the SPI clock speed after initialization but the method access_spi panics:

thread 'main' panicked at core/src/panicking.rs:223:5:
attempted to zero-initialize type `embedded_hal_bus::spi::exclusive::ExclusiveDevice<rppal::spi::Spi, rppal::gpio::pin::OutputPin, rppal::hal::Delay>`, which is invalid

The panic occurs while zero-initializing the SPI device:

let spi = core::mem::zeroed();

I'm on a Raspberry Pi using rppal as embedded-hal implementation and embedded-hal-bus as SpiDevice implementation.

I would suggest wrapping the SPI device in an Option<SPI>. This also allows the unsafe block to be removed. I will open a pull request for it.