drm/panel: simple: Skip error message on deferred probe

When enable_gpio is provided via an I2C or SPI expander, it may not be
available when panel-simple probes leading to the following error:

panel-simple panel: failed to request GPIO: -517

As this error message is not very useful to the end user, skip printing
it in the case of deferred probe.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1498857286-10820-1-git-send-email-festevam@gmail.com

drivers/gpu/drm/panel/panel-simple.c

@@ -315,7 +315,8 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
 						     GPIOD_OUT_LOW);
 	if (IS_ERR(panel->enable_gpio)) {
 		err = PTR_ERR(panel->enable_gpio);
-		dev_err(dev, "failed to request GPIO: %d\n", err);
+		if (err != -EPROBE_DEFER)
+			dev_err(dev, "failed to request GPIO: %d\n", err);
 		return err;
 	}