drivers: iio: dac: ad5592r: add gpio_chip names

Add array of explicit gpio names for the `gpiochip` structure of
ad5592r, mainly for debug purposes.

Since the gpios are configurable via the dts, generic names are
used.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://lore.kernel.org/r/20221117090130.51702-1-antoniu.miclaus@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>