net: fec_mxc: Avoid enable regulator failure

Change to regulator_set_enable_if_allowed to avoid enable failure,
in case same phy supply shared by multiple FEC controllers.

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/drivers/net/fec_mxc.c b/drivers/net/fec_mxc.c
index ac93767..90af18f 100644
--- a/drivers/net/fec_mxc.c
+++ b/drivers/net/fec_mxc.c
@@ -1310,7 +1310,7 @@
 
 #ifdef CONFIG_DM_REGULATOR
 	if (priv->phy_supply) {
-		ret = regulator_set_enable(priv->phy_supply, true);
+		ret = regulator_set_enable_if_allowed(priv->phy_supply, true);
 		if (ret) {
 			printf("%s: Error enabling phy supply\n", dev->name);
 			return ret;