ALSA: pcm: Create proc files only for non-empty preallocations

It makes little sense to create prealloc proc files for streams that
have the zero max size, which is a typical case for vmalloc buffers.
Skip the proc file creations to save resources in such a case.

Link: https://lore.kernel.org/r/20191105191007.18150-3-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_memory.c

@@ -203,6 +203,7 @@ static void snd_pcm_lib_preallocate_pages1(struct snd_pcm_substream *substream,
 	if (substream->dma_buffer.bytes > 0)
 		substream->buffer_bytes_max = substream->dma_buffer.bytes;
 	substream->dma_max = max;
+	if (max > 0)
 		preallocate_info_init(substream);
 }