iio: add HAS_IOMEM dependency to VF610_ADC

commit 005ce071 upstream.

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>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/iio/adc/Kconfig

@@ -233,6 +233,7 @@ config TWL6030_GPADC
 config VF610_ADC
 	tristate "Freescale vf610 ADC driver"
 	depends on OF
+	depends on HAS_IOMEM
 	help
 	  Say yes here to support for Vybrid board analog-to-digital converter.
 	  Since the IP is used for i.MX6SLX, the driver also support i.MX6SLX.