staging,lpc32xx_adc: Add dependency on HAS_IOMEM

On archs like S390 or um this driver cannot build nor work.
Make it depend on HAS_IOMEM to bypass build failures.

drivers/built-in.o: In function `lpc32xx_adc_probe':
drivers/staging/iio/adc/lpc32xx_adc.c:149: undefined reference to `devm_ioremap'
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/staging/iio/adc/Kconfig

@@ -103,6 +103,7 @@ config AD7280
 config LPC32XX_ADC
 	tristate "NXP LPC32XX ADC"
 	depends on ARCH_LPC32XX || COMPILE_TEST
+	depends on HAS_IOMEM
 	help
 	  Say yes here to build support for the integrated ADC inside the
 	  LPC32XX SoC. Note that this feature uses the same hardware as the