iio/adc/cc10001_adc.c: Fix !HAS_IOMEM build

Fixes:
drivers/built-in.o: In function `cc10001_adc_probe':
cc10001_adc.c:(.text+0x412e92): undefined reference to `devm_ioremap_resource'

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>