mtd: lpc32xx_slc: Make probe() return -EPROBE_DEFER if necessary

Via of_get_named_gpio(), wp_gpio can become -EPROBE_DEFER which now makes
probe() return -EPROBE_DEFER as well to wait until the gpio controller is
probed before trying to probe lpc32xx_slc again.
Signed-off-by: Roland Stigge <stigge@antcom.de>
Acked-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/lpc32xx_slc.c

@@ -821,6 +821,8 @@ static int __devinit lpc32xx_nand_probe(struct platform_device *pdev)
 		dev_err(&pdev->dev, "Missing platform data\n");
 		return -ENOENT;
 	}
+	if (host->ncfg->wp_gpio == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
 	if (gpio_is_valid(host->ncfg->wp_gpio) &&
 			gpio_request(host->ncfg->wp_gpio, "NAND WP")) {
 		dev_err(&pdev->dev, "GPIO not available\n");