ao_coreaudio: add a comment for ignoring returned sample count

Co-authored-by: sfan5 <sfan5@live.de>

audio/out/ao_coreaudio.c

@@ -89,6 +89,7 @@ static OSStatus render_cb_lpcm(void *ctx, AudioUnitRenderActionFlags *aflags,
 
     int64_t end = mp_time_ns();
     end += p->hw_latency_ns + ca_get_latency(ts) + ca_frames_to_ns(ao, frames);
+    // don't use the returned sample count since CoreAudio always expects full frames
     ao_read_data(ao, planes, frames, end);
     return noErr;
 }