phy: cadence: Sierra: Make "phy_clk" and "sierra_apb" optional resources

Certain platforms like TI J721E using Cadence Sierra Serdes
doesn't provide explicit phy_clk and reset (APB reset) control.
Make them optional here.
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

drivers/phy/cadence/phy-cadence-sierra.c

@@ -193,7 +193,7 @@ static int cdns_sierra_phy_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, sp);
 
-	sp->clk = devm_clk_get(dev, "phy_clk");
+	sp->clk = devm_clk_get_optional(dev, "phy_clk");
 	if (IS_ERR(sp->clk)) {
 		dev_err(dev, "failed to get clock phy_clk\n");
 		return PTR_ERR(sp->clk);
@@ -205,7 +205,7 @@ static int cdns_sierra_phy_probe(struct platform_device *pdev)
 		return PTR_ERR(sp->phy_rst);
 	}
 
-	sp->apb_rst = devm_reset_control_get(dev, "sierra_apb");
+	sp->apb_rst = devm_reset_control_get_optional(dev, "sierra_apb");
 	if (IS_ERR(sp->apb_rst)) {
 		dev_err(dev, "failed to get apb reset\n");
 		return PTR_ERR(sp->apb_rst);