ALSA: cs5535audio: check OLPC's Analog Input status vis GPIO

Checking the HPF register is irrelevant; HPF is secondary to the AI mode.
Instead, check for Analog Input mode via GPIO.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>