ALSA: core: Fix kernel-doc warnings

Several lines in sound/core.h get the kernel-doc warnings like

  ./include/sound/core.h:323: warning: No description found for parameter '...'

where we use define like foo(x, args...) and "args" isn't mentioned in
the comments.  As an easy workaround, use simple __VA_ARGS__ for VLA
in macros.

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