ALSA: pci: cs46xx: Fix set up buffer type properly

ALSA: pci: cs46xx: Fix set up buffer type properly

CS46xx driver switches the buffer depending on the number of periods,
and in some cases it switches to the own buffer without updating the
buffer type properly.  This may cause a problem with the mmap on
exotic architectures that require the own mmap call for the coherent
DMA buffer.

This patch addresses the potential breakage by replacing the buffer
setup with the proper macro.  It also simplifies the source code,
too.

Link: https://lore.kernel.org/r/20210809071829.22238-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>