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

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

In the recent fix commit a7d2bd4bc2c2 ("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.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>