gpio: mxc_gpio: change gpio index for i.MX8

Since the i.MX8 GPIO banks are indexed from 0 not 1 on other i.MX
platforms, so we have to adjust the index accordingly.

Signed-off-by: Adrian Alonso <adrian.alonso@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/drivers/gpio/mxc_gpio.c b/drivers/gpio/mxc_gpio.c
index c924e52..316dcc7 100644
--- a/drivers/gpio/mxc_gpio.c
+++ b/drivers/gpio/mxc_gpio.c
@@ -281,7 +281,10 @@
 	char name[18], *str;
 
 	banknum = plat->bank_index;
-	sprintf(name, "GPIO%d_", banknum + 1);
+	if (IS_ENABLED(CONFIG_ARCH_IMX8))
+		sprintf(name, "GPIO%d_", banknum);
+	else
+		sprintf(name, "GPIO%d_", banknum + 1);
 	str = strdup(name);
 	if (!str)
 		return -ENOMEM;