ALSA: memalloc: Fix regression with SNDRV_DMA_TYPE_CONTINUOUS

The recent code refactoring made the mmap of continuous pages to be
done via the own helper snd_dma_continuous_mmap() with
remap_pfn_range().  There I overlooked that dmab->addr isn't set for
the allocation with SNDRV_DMA_TYPE_CONTINUOUS.  This resulted always
in an error at mmap with this buffer type on the system such as
Intel SST Baytrail driver.

This patch fixes the regression by passing the correct address.

Fixes: 30b7ba69 ("ALSA: core: Add continuous and vmalloc mmap ops")
Reported-by: NHans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/8d6674da-7d7b-803e-acc9-7de6cb1223fa@redhat.com
Link: https://lore.kernel.org/r/20210801113801.31290-1-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

sound/core/memalloc.c

@@ -215,7 +215,7 @@ static int snd_dma_continuous_mmap(struct snd_dma_buffer *dmab,
 				   struct vm_area_struct *area)
 {
 	return remap_pfn_range(area, area->vm_start,
-			       dmab->addr >> PAGE_SHIFT,
+			       page_to_pfn(virt_to_page(dmab->area)),
 			       area->vm_end - area->vm_start,
 			       area->vm_page_prot);
 }