iio: adc: ingenic: Use devm_platform_ioremap_resource

Replaces local boilerplate.  Identified by coccinelle.
CHECK   drivers/iio/adc/ingenic-adc.c
drivers/iio/adc/ingenic-adc.c:449:1-10: WARNING: Use devm_platform_ioremap_resource for adc -> base

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Artur Rojek <contact@artur-rojek.eu>