ALSA: hda/conexant - Clear unsol events on unused pins

It seems that Lenovo machines (or codec chip itself?) leave the unsol
event tags and the enablement-flag from other pins bogusly even on the
unused pins.  Although this shouldn't be too critical, it's better to
clear them up sanely.

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