staging: comedi: ni_at_a2150: checkpatch.pl cleanup (break not useful)

Fix the checkpatch.pl warning:

WARNING: break is not useful after a goto or return
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_at_a2150.c

@@ -681,7 +681,6 @@ static int a2150_set_chanlist(struct comedi_device *dev,
 		break;
 	default:
 		return -1;
-		break;
 	}
 
 	return 0;