Fix some clippy lints triggered by rust beta

[jannic]

No description provided.

[jannic]

Fails on older rust versions with:

unknown lint: `clippy::missing_transmute_annotations`

I wonder what's the best way to handle this:

• also add #[allow(unknown_lints)]
• add type annotations to all transmute calls to fix the lint (a lot of noise, IMHO)
• do nothing and live with the clippy warning in beta for now

[jannic]

I think I was too quick with my suggestion to add #![allow(clippy::missing_transmute_annotations)] - the transmutes nightly clippy warns about are actually buggy. 😨

Eg.:

warning: transmute used without annotations
   --> rp2040-hal/src/gpio/pin/pin_sealed.rs:144:37
    |
144 |                     0 => core::mem::transmute(&qspi.gpio_qspi_sclk()),
    |                                     ^^^^^^^^^ help: consider adding missing annotations: `transmute::<&&rp2040_pac::generic::Reg<rp2040_pac::pads_qspi::gpio_qspi_sclk::GPIO_QSPI_SCLK_SPEC>, &rp2040_pac::generic::Reg<rp2040_pac::pads_bank0::gpio::GPIO_SPEC>>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_transmute_annotations
    = note: `#[warn(clippy::missing_transmute_annotations)]` on by default

Note that it transmutes from &&Reg to &Reg which is obviously bogus.
I'll fix this in a separate ticket.