ALSA: memalloc: Store snd_dma_buffer.addr for continuous pages, too

In the recent fix commit eda80d7c ("ALSA: memalloc: Fix regression
with SNDRV_DMA_TYPE_CONTINUOUS"), we replaced the pfn argument of the
remap_page_pfn() call from the uninitialized dmab->addr.  It was the
right fix, but it'd be more generic if we actually initialize
dmab->area for SNDRV_DMA_TYPE_CONTINOUS, too.  e.g. the field is used
in the common snd_sgbuf_get_addr(), too.

This patch adds the initialization of addr field and does revert of
the previous change to refer to it again in the mmap call.

Link: https://lore.kernel.org/r/20210804074125.8170-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/memalloc.c

@@ -242,8 +242,11 @@ EXPORT_SYMBOL(snd_sgbuf_get_chunk_size);
 static void *snd_dma_continuous_alloc(struct snd_dma_buffer *dmab, size_t size)
 {
 	gfp_t gfp = snd_mem_get_gfp_flags(dmab, GFP_KERNEL);
+	void *p = alloc_pages_exact(size, gfp);
 
-	return alloc_pages_exact(size, gfp);
+	if (p)
+		dmab->addr = page_to_phys(virt_to_page(p));
+	return p;
 }
 
 static void snd_dma_continuous_free(struct snd_dma_buffer *dmab)
@@ -255,7 +258,7 @@ static int snd_dma_continuous_mmap(struct snd_dma_buffer *dmab,
 				   struct vm_area_struct *area)
 {
 	return remap_pfn_range(area, area->vm_start,
-			       page_to_pfn(virt_to_page(dmab->area)),
+			       dmab->addr >> PAGE_SHIFT,
 			       area->vm_end - area->vm_start,
 			       area->vm_page_prot);
 }