staging: comedi: cb_das16_cs: fix analog output subdevice init

The analog output subdevice is only available on the -AO version
of the DAS16/16 device and the number of channels is provided in
the boardinfo. Make sure the subdevice is marked as unused for
devices that do not support the analog out.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/cb_das16_cs.c

@@ -509,6 +509,8 @@ static int das16cs_attach(struct comedi_device *dev,
 		s->range_table = &range_bipolar10;
 		s->insn_write = &das16cs_ao_winsn;
 		s->insn_read = &das16cs_ao_rinsn;
+	} else {
+		s->type = COMEDI_SUBD_UNUSED;
 	}
 
 	s = dev->subdevices + 2;