Use cyw43_delay_ms() in cyw43_spi_reset() instead of sleep_ms()

[mbrase]

Since cyw43_spi_reset() may be executed from an async context, we should use cyw43_delay_ms() instead of sleep_ms(). This is particularly a problem when using the async_context_threadsafe_background backend, because sleep_ms() will assert in an ISR.

[mbrase]

For additional context, this is the code that I'm running that crashes without this patch:

#include "pico/cyw43_arch.h"

void StartBlinkingLed() {
  static bool state = false;
  static async_at_time_worker_t worker = {
      .next = nullptr,
      .do_work =
          [](async_context_t* context, async_at_time_worker_t* worker) {
            bool& state = *static_cast<bool*>(worker->user_data);
            state = !state;
            cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, state);
            async_context_add_at_time_worker_in_ms(context, worker, 1000);
          },
      .next_time = 0,
      .user_data = &state,
  };
  cyw43_arch_init();
  async_context_add_at_time_worker_in_ms(
      cyw43_arch_async_context(), &worker, 50);
}

[peterharperuk]

I think this should be ok. Ran some tests and everything worked.