ALSA: ac97: kconfig: Remove select of undefined symbol AC97

The AC97_BUS_NEW Kconfig symbol selects the globally undefined symbol
AC97.

Robert Jarzmik confirmed in https://lkml.org/lkml/2018/2/7/96

 that the
select was put in by mistake and can be safely removed, with no other
changes required. Remove it.

Fixes: 74426fbf ("ALSA: ac97: add an ac97 bus")
Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>