mfd: cros_ec: Check DT node for usbpd-notify add

Add a check to ensure there is indeed an EC device tree entry before
adding the cros-usbpd-notify device. This covers configs where both
CONFIG_ACPI and CONFIG_OF are defined, but the EC device is defined
using device tree and not in ACPI.

Fixes: 4602dce0361e ("mfd: cros_ec: Add cros-usbpd-notify subdevice")
Signed-off-by: Prashant Malani <[e-mail]>
Tested-by: Enric Balletbo i Serra <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/cros_ec_dev.c

···
 	 * explicitly added on platforms that don't have the PD notifier ACPI
 	 * device entry defined.
 	 */
-	if (IS_ENABLED(CONFIG_OF)) {
+	if (IS_ENABLED(CONFIG_OF) && ec->ec_dev->dev->of_node) {
 		if (cros_ec_check_features(ec, EC_FEATURE_USB_PD)) {
 			retval = mfd_add_hotplug_devices(ec->dev,
 					cros_usbpd_notify_cells,