ALSA: pcm - fix page conversion on non-coherent MIPS arch

The non-coherent MIPS arch doesn't give the correct address by a simple
virt_to_page() for pages allocated via dma_alloc_coherent().

Original patch by Wu Zhangjin <wuzj@lemote.com>.
[Ralf mentioned: "The origins of this patch go back far further.
 The oldest patch I could find which is a superset of this was written
 by Atsushi Nemoto and various incarnations of it have been sumitted
 to and reject by me a number of times through the years."]
A proper check of the buffer allocation type was added to avoid the
wrong conversion.

Note that this doesn't fix perfectly: the pages should be marked with
proper pgprot value.  This will be done in a future implementation like
the conversion to dma_mmap_coherent().
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -3066,6 +3066,10 @@ static inline struct page *
 snd_pcm_default_page_ops(struct snd_pcm_substream *substream, unsigned long ofs)
 {
 	void *vaddr = substream->runtime->dma_area + ofs;
+#if defined(CONFIG_MIPS) && defined(CONFIG_DMA_NONCOHERENT)
+	if (substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)
+		return virt_to_page(CAC_ADDR(vaddr));
+#endif
 	return virt_to_page(vaddr);
 }