[ALSA] remove bogus match method for ac97_bus

AC97 Codec
The bus_id is initialized with a generic identifier string which is not
really useful for proper driver matching.  Let the driver decide what it
needs via its probe method instead.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>