ALSA: hdspm - Fix S/PDIF Sync status and frequency on RME AIO

This is a left-over mistake from old code, the correct register offset is
provided in kcontrol->private_value, not in the index.
Cf. RayDAT case, where it has already been corrected.

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>