rk_iodomain: Do not require optional FDT properties.

The regulatos in the list are documented as optional, do not require them.

MFC after:	2 weeks
Reviewed by:	andrew
Differential Revision:	https://reviews.freebsd.org/D50101

Author: strejda

sys/arm64/rockchip/rk_iodomain.c

@@ -163,11 +163,16 @@ rk_iodomain_set(struct rk_iodomain_softc *sc)
 	regulator_t supply;
 	uint32_t reg = 0;
 	uint32_t mask = 0;
-	int uvolt, i;
+	int uvolt, i, rv;
 
 	for (i = 0; i < sc->conf->nsupply; i++) {
-		if (regulator_get_by_ofw_property(sc->dev, sc->node,
-		    sc->conf->supply[i].name, &supply) != 0) {
+		rv = regulator_get_by_ofw_property(sc->dev, sc->node,
+		    sc->conf->supply[i].name, &supply);
+
+		if (rv == ENOENT)
+			continue;
+
+		if (rv != 0) {
 			device_printf(sc->dev,
 			    "Cannot get property for regulator %s\n",
 			    sc->conf->supply[i].name);