mtd: lpc32xx_slc: Make wp gpio optional

This patch supports missing wp gpio.

Signed-off-by: Alexandre Pereira da Silva <[e-mail]>
Signed-off-by: Roland Stigge <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/nand/lpc32xx_slc.c

···
 	uint32_t rhold;
 	uint32_t rsetup;
 	bool use_bbt;
-	unsigned wp_gpio;
+	int wp_gpio;
 	struct mtd_partition *parts;
 	unsigned num_parts;
 };
···
  */
 static void lpc32xx_wp_enable(struct lpc32xx_nand_host *host)
 {
-	gpio_set_value(host->ncfg->wp_gpio, 0);
+	if (gpio_is_valid(host->ncfg->wp_gpio))
+		gpio_set_value(host->ncfg->wp_gpio, 0);
 }
 
 /*
···
  */
 static void lpc32xx_wp_disable(struct lpc32xx_nand_host *host)
 {
-	gpio_set_value(host->ncfg->wp_gpio, 1);
+	if (gpio_is_valid(host->ncfg->wp_gpio))
+		gpio_set_value(host->ncfg->wp_gpio, 1);
 }
 
 /*
···
 		dev_err(&pdev->dev, "Missing platform data\n");
 		return -ENOENT;
 	}
-	if (gpio_request(host->ncfg->wp_gpio, "NAND WP")) {
+	if (gpio_is_valid(host->ncfg->wp_gpio) &&
+			gpio_request(host->ncfg->wp_gpio, "NAND WP")) {
 		dev_err(&pdev->dev, "GPIO not available\n");
 		return -EBUSY;
 	}