spi: mpc52xx: Use gpio_is_valid()

Replace the manual validity checks for the GPIO with the
gpio_is_valid().

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-mpc52xx.c

@@ -447,7 +447,7 @@ static int mpc52xx_spi_probe(struct platform_device *op)
 
 		for (i = 0; i < ms->gpio_cs_count; i++) {
 			gpio_cs = of_get_gpio(op->dev.of_node, i);
-			if (gpio_cs < 0) {
+			if (!gpio_is_valid(gpio_cs)) {
 				dev_err(&op->dev,
 					"could not parse the gpio field in oftree\n");
 				rc = -ENODEV;