staging: comedi: dt2811: fix a precedence bug

Bitwise | has higher precedence than ?: so we need to add some
parenthesis for this to work as intended.

Fixes: 7c957409 ('staging: comedi: dt2811: simplify A/D reference configuration')
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/dt2811.c

@@ -588,8 +588,8 @@ static int dt2811_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	s = &dev->subdevices[0];
 	s->type		= COMEDI_SUBD_AI;
 	s->subdev_flags	= SDF_READABLE |
-			  (it->options[2] == 1) ? SDF_DIFF :
-			  (it->options[2] == 2) ? SDF_COMMON : SDF_GROUND;
+			  ((it->options[2] == 1) ? SDF_DIFF :
+			   (it->options[2] == 2) ? SDF_COMMON : SDF_GROUND);
 	s->n_chan	= (it->options[2] == 1) ? 8 : 16;
 	s->maxdata	= 0x0fff;
 	s->range_table	= board->is_pgh ? &dt2811_pgh_ai_ranges