iio: dac: ad5755: make use of of_device_id table

iio: dac: ad5755: make use of of_device_id table

Store pointers to chip info (struct ad5755_chip_info) in driver match
data, instead of enum, so every value will be != 0, populate the
of_device_id table and use it in driver.  Even though it is one change,
it gives multiple benefits:
1. Allows to use spi_get_device_match_data() dropping local 'type'
   variable.
2. Makes both ID tables usable, so kernel can match via any of these
   methods.
3. Code is more obvious as both tables are properly filled.
4. Fixes W=1 warning:
   ad5755.c:866:34: error: unused variable 'ad5755_of_match' [-Werror,-Wunused-const-variable]

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240413154511.52576-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>