CTL_STATUS_t ctl_spi_set_speed(CTL_SPI_DEVICE_t *self, unsigned long speed);
ctl_spi_set_speed sets the SPI bus frequency to use for the device self to speed hertz.
Please refer to ctl_spi_set_protocol for a description of when protocol parameters are validated.
ctl_spi_set_speed returns a standard status code.