iio: sx9310: Fix access to variable DT array

iio: sx9310: Fix access to variable DT array

With the current code, we want to read 4 entries from DT array
"semtech,combined-sensors". If there are less, we silently fail as
of_property_read_u32_array() returns -EOVERFLOW.

First count the number of entries and if between 1 and 4, collect the
content of the array.

Fixes: 5b19ca2c78a0 ("iio: sx9310: Set various settings from DT")
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210326184603.251683-2-gwendal@chromium.org
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>