ALSA: pcm: fix the comments that refers to kernel-doc

The markup inside the #if 0 comment actually refers to a
kernel-doc markup. As we're getting rid of DocBook update it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>