ALSA: hda - Fix max amp cap calculation for IDT/STAC codecs

The commit afbd9b84
    ALSA: hda - Limit the amp value to write
introduced a regression for codec setups with amp offsets like IDT/STAC
codecs.  The limit value should be a raw value without offset calculation.

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