hwrng: ba431 - Add dependency on HAS_IOMEM

The ba431 driver depends on HAS_IOMEM and this was missing from
the Kconfig file.
Reported-by: Nkernel test robot <lkp@intel.com>
Fixes: 0289e9be ("hwrng: ba431 - add support for BA431 hwrng")
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/Kconfig

@@ -76,6 +76,7 @@ config HW_RANDOM_ATMEL
 
 config HW_RANDOM_BA431
 	tristate "Silex Insight BA431 Random Number Generator support"
+	depends on HAS_IOMEM
 	default HW_RANDOM
 	help
 	  This driver provides kernel-side support for the Random Number