gpio: mxc: Use devm_clk_get_optional instead of devm_clk_get

i.MX SoC's GPIO clock is optional, so it is better to use
devm_clk_get_optional instead of devm_clk_get.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-mxc.c

@@ -435,12 +435,9 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 		return port->irq;
 
 	/* the controller clock is optional */
-	port->clk = devm_clk_get(&pdev->dev, NULL);
-	if (IS_ERR(port->clk)) {
-		if (PTR_ERR(port->clk) == -EPROBE_DEFER)
-			return -EPROBE_DEFER;
-		port->clk = NULL;
-	}
+	port->clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(port->clk))
+		return PTR_ERR(port->clk);
 
 	err = clk_prepare_enable(port->clk);
 	if (err) {