iio: adc: stm32-dfsdm: Use devm_platform_get_and_ioremap_resource()

Make use of devm_platform_get_and_ioremap_resource() provided by
driver core platform instead of duplicated analogue, dev_err() is
removed because it has been done in devm_ioremap_resource().

Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Link: https://lore.kernel.org/r/20200918083142.32816-1-bobo.shaobowang@huawei.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>