Zero not a valid value for f in Port.Connect

[nathan-osman]

Describe the bug According to the documentation for spi.Port.Connect(), 0 is a valid value to use for specifying SPI speed:

...Use 0 for f if there is no known maximum value for this device...

However, I instead receive an error when providing 0:

panic: sysfs-spi: invalid speed 0Hz; minimum supported clock is 100Hz; did you forget to multiply by physic.MegaHertz?

To Reproduce Steps to reproduce the behavior:

1. Enter program

package main

import (
  "periph.io/x/host/v3"
  "periph.io/x/conn/v3/spi/spireg"
)

func main() {
  host.Init()
  p, err := spireg.Open("0")
  if err != nil {
    panic(err)
  }
  defer p.Close()
  c, err := p.Connect(0, spi.Mode0, 8)
  if err != nil {
    panic(err)
  }
}

2. Run it.
3. See error

Expected behavior No error, and the connection to the SPI device succeeds.

Platform (please complete the following information):

• OS: Raspbian GNU/Linux 12 with armv7l kernel
• Board: Raspberry Pi Zero 2W

Additional thoughts Perhaps if this is not intended to be supported behavior, the documentation should be updated to remove the 0 option.