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 <[e-mail]>
Acked-by: Alexandre Pereira da Silva <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/nand/lpc32xx_slc.c

···
 		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");