iio: ltr501: mark register holding upper 8 bits of ALS_DATA{0,1} and PS_DATA as volat...

iio: ltr501: mark register holding upper 8 bits of ALS_DATA{0,1} and PS_DATA as volatile, too

The regmap is configured for 8 bit registers, uses a RB-Tree cache and
marks several registers as volatile (i.e. do not cache).

The ALS and PS data registers in the chip are 16 bit wide and spans
two regmap registers. In the current driver only the base register is
marked as volatile, resulting in the upper register only read once.

Further the data sheet notes:

| When the I2C read operation starts, all four ALS data registers are
| locked until the I2C read operation of register 0x8B is completed.

Which results in the registers never update after the 2nd read.

This patch fixes the problem by marking the upper 8 bits of the ALS
and PS registers as volatile, too.

Fixes: 2f2c96338afc ("iio: ltr501: Add regmap support.")
Reported-by: Oliver Lang <Oliver.Lang@gossenmetrawatt.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Nikita Travkin <nikita@trvn.ru> # ltr559
Link: https://lore.kernel.org/r/20210610134619.2101372-2-mkl@pengutronix.de
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>