iio: dac: stm32-dac: Make use of the helper function devm_platform_ioremap_resource()

Use the devm_platform_ioremap_resource() helper instead of
calling platform_get_resource() and devm_ioremap_resource()
separately

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Link: https://lore.kernel.org/r/20210908105638.1525-1-caihuoqing@baidu.com


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