ALSA: pcm: use exit controlled loop in snd_pcm_playback_silence()

We already know that `frames` is greater than zero, because we just
checked it. So we don't need to check the loop condition on the first
iteration.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230505155244.2312199-7-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -123,14 +123,14 @@ void snd_pcm_playback_silence(struct snd_pcm_substream *substream, snd_pcm_ufram
 	if (frames == 0)
 		return;
 	ofs = (runtime->silence_start + runtime->silence_filled) % runtime->buffer_size;
-	while (frames > 0) {
+	do {
 		transfer = ofs + frames > runtime->buffer_size ? runtime->buffer_size - ofs : frames;
 		err = fill_silence_frames(substream, ofs, transfer);
 		snd_BUG_ON(err < 0);
 		runtime->silence_filled += transfer;
 		frames -= transfer;
 		ofs = 0;
-	}
+	} while (frames > 0);
 	snd_pcm_dma_buffer_sync(substream, SNDRV_DMA_SYNC_DEVICE);
 }