hwrng: stm32 - Fix dependencies for !HAS_IOMEM archs

Not every arch has io memory.
So, unbreak the build by fixing the dependencies.
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/Kconfig

@@ -372,6 +372,7 @@ config HW_RANDOM_XGENE
 config HW_RANDOM_STM32
 	tristate "STMicroelectronics STM32 random number generator"
 	depends on HW_RANDOM && (ARCH_STM32 || COMPILE_TEST)
+	depends on HAS_IOMEM
 	help
 	  This driver provides kernel-side support for the Random Number
 	  Generator hardware found on STM32 microcontrollers.