hdspmixer: Fix read/write from/to preset files on MADI-like cards

hdspmixer: Fix read/write from/to preset files on MADI-like cards

The old hdspmixer (prior to e24e56795ea57e3dd7da45063ab71f04e231192d,
that is pre-1.0.24) has used the hard-coded value "14" for
reading/storing 14 ints from/to preset files, however, it's actually
HDSP_MAX_DEST that should be used.

HDSP_MAX_DEST was bumped from 14 to 32 to allow for MADI cards (32
stereo pairs equal 64 output channels on MADI cards)

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