zephyr: ioex: Fix crash when cros ioex drivers disabled
zephyr: ioex: Fix crash when cros ioex drivers disabled

EC crash in ioex_init() if the following Kconfig options are set:
    CONFIG_PLATFORM_EC_IOEX=y
    CONFIG_PLATFORM_EC_IOEX_CROS_DRV=n

returning EC_SUCCESS if CONFIG_PLATFORM_EC_IOEX_CROS_DRV is not enabled.

BUG=none
BRANCH=none
TEST=zmake testall

Signed-off-by: Rajesh Kumar <ef973afabdaa06670be7215ef6ba2acd6d71d568@intel.com>
Change-Id: I51e83b14e46efd605e23922c9025a1aaa03f1098
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3384475
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Commit-Queue: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec