gpio: mxc: add check to return defer probe if clock tree NOT ready

commit a329bbe707cee2cf8c660890ef2ad0d00ec7e8a3 upstream.

On i.MX8MQ platform, clock driver uses platform driver
model and it is probed after GPIO driver, so when GPIO
driver fails to get clock, it should check the error type
to decide whether to return defer probe or just ignore
the clock operation.

Fixes: 2808801aab8a ("gpio: mxc: add clock operation")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpio-mxc.c

@@ -438,8 +438,11 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 
 	/* the controller clock is optional */
 	port->clk = devm_clk_get(&pdev->dev, NULL);
-	if (IS_ERR(port->clk))
+	if (IS_ERR(port->clk)) {
+		if (PTR_ERR(port->clk) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
 		port->clk = NULL;
+	}
 
 	err = clk_prepare_enable(port->clk);
 	if (err) {