ALSA: hda - Add probe_mask quirk for Medion MD96630

Medion MD96630 has ALC268 codec on slot#2 although it's not used
for any purpose.  This codec conflicts with the primiary codec ALC888
on slot#0, and gives mixer errors.

This patch adds a corresponding entry to probe_mask blacklist.

Reference: Novell bnc#412528
	https://bugzilla.novell.com/show_bug.cgi?id=412528

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