staging: comedi: ni_at_a2150: range check board index

The "ni_at_a2150" driver determines the board type by calling
`a2150_probe()`.  This reads a register and converts it to a board index
in the range 0 to 3.  However, the board table array it indexes into
(`a2150_boards[]`) only has 2 entries.  Return an error from the
Comedi driver "attach" handler `a2150_attach()` if the probed board
index is beyond the end of the array.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_at_a2150.c

@@ -705,7 +705,11 @@ static int a2150_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	if (ret)
 		return ret;
 
-	dev->board_ptr = a2150_boards + a2150_probe(dev);
+	i = a2150_probe(dev);
+	if (i >= ARRAY_SIZE(a2150_boards))
+		return -ENODEV;
+
+	dev->board_ptr = a2150_boards + i;
 	thisboard = comedi_board(dev);
 	dev->board_name = thisboard->name;