net: stmmac: dwmac-rk: Don't fail if phy regulator is absent

The devicetree binding lists the phy phy as optional. As such, the
driver should not bail out if it can't find a regulator. Instead it
should just skip the remaining regulator related code and continue
on normally.

Skip the remainder of phy_power_on() if a regulator supply isn't
available. This also gets rid of the bogus return code.

Fixes: 2e12f536 ("net: stmmac: dwmac-rk: Use standard devicetree property for phy regulator")
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c

@@ -1194,10 +1194,8 @@ static int phy_power_on(struct rk_priv_data *bsp_priv, bool enable)
 	int ret;
 	struct device *dev = &bsp_priv->pdev->dev;
 
-	if (!ldo) {
-		dev_err(dev, "no regulator found\n");
-		return -1;
-	}
+	if (!ldo)
+		return 0;
 
 	if (enable) {
 		ret = regulator_enable(ldo);