iio: adc: meson_saradc: use devm_platform_ioremap_resource

Avoid local boilerplate.
Suggested by coccinelle via coccicheck.
CHECK   drivers/iio/adc/meson_saradc.c
drivers/iio/adc/meson_saradc.c:1218:1-5: WARNING: Use devm_platform_ioremap_resource for base

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>