drivers: gpio: Fix dev_read_addr error check

dev_read_addr returns FDT_ADDR_T_NONE (-1) in case of error
and not 0.

Signed-off-by: Francois Berder <fberder@outlook.fr>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/gpio/gpio-fxl6408.c

@@ -273,7 +273,7 @@ static int fxl6408_probe(struct udevice *dev)
 	u32 val32;
 
 	addr = dev_read_addr(dev);
-	if (addr == 0)
+	if (addr == FDT_ADDR_T_NONE)
 		return -EINVAL;
 
 	info->addr = addr;

drivers/gpio/pca953x_gpio.c

@@ -312,7 +312,7 @@ static int pca953x_probe(struct udevice *dev)
 	u8 val[MAX_BANK];
 
 	addr = dev_read_addr(dev);
-	if (addr == 0)
+	if (addr == FDT_ADDR_T_NONE)
 		return -ENODEV;
 
 	info->addr = addr;