pinctrl: rockchip: constify rockchip_pin_ctrl for RK3328

There's no need to modify private data from the controller, so let's
make that struct const.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/pinctrl/rockchip/pinctrl-rk3328.c b/drivers/pinctrl/rockchip/pinctrl-rk3328.c
index dd0dc2e..1834df6 100644
--- a/drivers/pinctrl/rockchip/pinctrl-rk3328.c
+++ b/drivers/pinctrl/rockchip/pinctrl-rk3328.c
@@ -330,7 +330,7 @@
 			     0),
 };
 
-static struct rockchip_pin_ctrl rk3328_pin_ctrl = {
+static const struct rockchip_pin_ctrl rk3328_pin_ctrl = {
 	.pin_banks		= rk3328_pin_banks,
 	.nr_banks		= ARRAY_SIZE(rk3328_pin_banks),
 	.grf_mux_offset		= 0x0,