This silences the following sparse warning:
sparse: alsa_write.c:128:31: warning: Using plain integer as NULL pointer
period_time = pad->buffer_time * 250; /* buffer time / 4 */
msg = "could not set period time";
ret = snd_pcm_hw_params_set_period_time_near(pad->handle, hwparams,
period_time = pad->buffer_time * 250; /* buffer time / 4 */
msg = "could not set period time";
ret = snd_pcm_hw_params_set_period_time_near(pad->handle, hwparams,