net: stmmac: remove redundant null check before clk_disable_unprepare()

Because clk_prepare_enable() and clk_disable_unprepare() already checked
NULL clock parameter, so the additional checks are unnecessary, just
remove them.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -788,8 +788,7 @@ static int stmmac_init_ptp(struct stmmac_priv *priv)
 
 static void stmmac_release_ptp(struct stmmac_priv *priv)
 {
-	if (priv->plat->clk_ptp_ref)
-		clk_disable_unprepare(priv->plat->clk_ptp_ref);
+	clk_disable_unprepare(priv->plat->clk_ptp_ref);
 	stmmac_ptp_unregister(priv);
 }
 
@@ -5108,8 +5107,7 @@ int stmmac_suspend(struct device *dev)
 		stmmac_mac_set(priv, priv->ioaddr, false);
 		pinctrl_pm_select_sleep_state(priv->device);
 		/* Disable clock in case of PWM is off */
-		if (priv->plat->clk_ptp_ref)
-			clk_disable_unprepare(priv->plat->clk_ptp_ref);
+		clk_disable_unprepare(priv->plat->clk_ptp_ref);
 		clk_disable_unprepare(priv->plat->pclk);
 		clk_disable_unprepare(priv->plat->stmmac_clk);
 	}