iio: light: fix vcnl4000 devicetree hooks

Since commit ebd457d5 ("iio: light: vcnl4000 add devicetree hooks")
the of_match_table is supported but the data shouldn't be a string.
Instead it shall be one of 'enum vcnl4000_device_ids'. Also the matching
logic for the vcnl4020 was wrong. Since the data retrieve mechanism is
still based on the i2c_device_id no failures did appeared till now.

Fixes: ebd457d5 ("iio: light: vcnl4000 add devicetree hooks")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Angus Ainslie (Purism) <angus@akkea.ca>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>