ALSA: msnd: Use proper mmap method

The old ISA MSND driver basically maps the iomem as the DMA buffer.
For this type of buffer, we have already the standard mmap helper,
snd_pcm_lib_mmap_iomem().  Correct the PCM info, set the DMA address
and use the standard helper for handling the mmap on all architectures
properly.

Link: https://lore.kernel.org/r/20210809140532.11006-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>