iio: add HAS_IOMEM dependency to VF610_ADC

Ran into this on UML:

drivers/built-in.o: In function `vf610_adc_probe':
drivers/iio/adc/vf610_adc.c:744: undefined reference to `devm_ioremap_resource'

devm_ioremap_resource() is defined only when HAS_IOMEM is selected.
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/Kconfig

@@ -372,6 +372,7 @@ config TWL6030_GPADC
 config VF610_ADC
 	tristate "Freescale vf610 ADC driver"
 	depends on OF
+	depends on HAS_IOMEM
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 	help