Modify NumUpdates for different sample rates instead of UpdateSize

Not that this really changes anything since the CoreAudio backend doesn't honor
the ALCdevice's buffer metrics, nor accurately report the device's actual
metrics. But it clears up warnings from a non-multiple-of-four update size if
the sample rate causes it to change.

Alc/backends/coreaudio.c

@@ -238,7 +238,7 @@ static ALCboolean ca_reset_playback(ALCdevice *device)
 
     if(device->Frequency != streamFormat.mSampleRate)
     {
-        device->UpdateSize = (ALuint)((ALuint64)device->UpdateSize *
+        device->NumUpdates = (ALuint)((ALuint64)device->NumUpdates *
                                       streamFormat.mSampleRate /
                                       device->Frequency);
         device->Frequency = streamFormat.mSampleRate;