ALSA: rme9652: fix a missing comma in channel_map_9636_ds[]

The lack of comma leads to the wrong channel for an SPDIF channel.
Unfortunately this wasn't caught by compiler because it's still a
valid expression.

Reported-by: Alexander Aristov <aristov.alexander@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>