iio: adc: rockchip_saradc: use = { } instead of memset()

Use { } instead of memset() to zero-initialize stack memory to simplify
the code.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250611-iio-zero-init-stack-with-instead-of-memset-v1-5-ebb2d0a24302@baylibre.com


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