ALSA: pci: rme: Set up buffer type properly

Although the regression of the mmap was fixed in the recent commit
dc0dc8a7

 ("ALSA: pcm: Fix mmap breakage without explicit buffer
setup"), RME9652 and HDSP drivers have still potential issues with
their mmap handling.  Namely, they use the default mmap handler
without the standard buffer preallocation, and PCM core wouldn't use
the coherent DMA mapping.  It's practically OK on x86, but on some
exotic architectures, it wouldn't work.

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/20210809071829.22238-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>