if i flash a basic firmware that prints Hello World via usb cdc/acm using the stm toolchain it works. if i use any usb_* example from embassy-rs i get various error numbers in my dmesg:
```
[13113.592919] usb 1-2.4.1: USB disconnect, device number 101
[13115.305599] usb 1-2.4.1: new full-speed USB device number 102 using xhci_hcd
[13115.446617] usb 1-2.4.1: device descriptor read/64, error -71
[13115.688619] usb 1-2.4.1: device descriptor read/64, error -71
[13115.859594] usb 1-2.4.1: new full-speed USB device number 103 using xhci_hcd
[13116.001617] usb 1-2.4.1: device descriptor read/64, error -71
[13116.249607] usb 1-2.4.1: device descriptor read/64, error -71
[13116.356667] usb 1-2.4-port1: attempt power cycle
[13116.942584] usb 1-2.4.1: new full-speed USB device number 104 using xhci_hcd
[13127.308551] usb 1-2.4.1: device descriptor read/8, error -110
[13142.150274] usb 1-2.4.1: device descriptor read/8, error -32
[13145.773241] usb 1-2.4.1: new full-speed USB device number 106 using xhci_hcd
[13867.766963] usb 1-2.2: USB disconnect, device number 64
```
the errors apparently change based on the assigned device class, but they're not really consistent. i observed error -71, -110 and -32.

assuming that the embassy-usb implementation is correct i guess the issue lies in my clocks.

```
let mut clocks = Config::default();
    // set the internal clock to run at max (80MHz)
    clocks.rcc.hsi = true;
    clocks.rcc.hse = Some(embassy_stm32::rcc::Hse {
        freq: Hertz(8_000_000),
        mode: embassy_stm32::rcc::HseMode::Oscillator,
    });
    clocks.rcc.pll = Some(embassy_stm32::rcc::Pll {
        source: embassy_stm32::rcc::PllSource::HSE,
        mul: embassy_stm32::rcc::PllMul::MUL20,
        divp: Some(embassy_stm32::rcc::PllPDiv::DIV7),
        divq: Some(embassy_stm32::rcc::PllQDiv::DIV2),
        divr: Some(embassy_stm32::rcc::PllRDiv::DIV2),
        prediv: embassy_stm32::rcc::PllPreDiv::DIV1,
    });
    // USB
    clocks.rcc.pllsai1 = Some(embassy_stm32::rcc::Pll {
        source: embassy_stm32::rcc::PllSource::HSE,
        prediv: embassy_stm32::rcc::PllPreDiv::DIV1,
        mul: embassy_stm32::rcc::PllMul::MUL12,
        divp: Some(embassy_stm32::rcc::PllPDiv::DIV7),
        divq: Some(embassy_stm32::rcc::PllQDiv::DIV2),
        divr: Some(embassy_stm32::rcc::PllRDiv::DIV2),
    });
    clocks.rcc.pllsai2 = Some(embassy_stm32::rcc::Pll {
        source: embassy_stm32::rcc::PllSource::HSE,
        prediv: embassy_stm32::rcc::PllPreDiv::DIV1,
        mul: embassy_stm32::rcc::PllMul::MUL8,
        divp: Some(embassy_stm32::rcc::PllPDiv::DIV7),
        divq: None,
        divr: Some(embassy_stm32::rcc::PllRDiv::DIV2),
    });
    clocks.rcc.mux.clk48sel = embassy_stm32::rcc::mux::Clk48sel::PLLSAI1_Q;
    clocks.rcc.sys = embassy_stm32::rcc::Sysclk::HSE;
    clocks.rcc.ahb_pre = embassy_stm32::rcc::AHBPrescaler::DIV2;
    clocks.rcc.apb1_pre = embassy_stm32::rcc::APBPrescaler::DIV1;
    clocks.rcc.apb2_pre = embassy_stm32::rcc::APBPrescaler::DIV1;
    clocks.rcc.mux.adcsel = embassy_stm32::rcc::mux::Adcsel::SYS;
```

can anyone spot any obvious mistake?