iio: adc: ad7124: Benefit of dev = indio_dev->dev.parent in ad7124_parse_channel_config()

Since commit a6eaf02b ("iio: adc: ad7124: Switch from of specific to
fwnode based property handling") the function
ad7124_parse_channel_config() has a parameter `dev` that holds
the value `indio_dev->dev.parent`. Make use of that to shorten two code
lines.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://patch.msgid.link/v7l2skqj65vbku3ebjsfndfj3atl6iqpodamios2do6q6kcagf@whmuir6fwede


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