pinctrl: rockchip: constify rockchip_pin_ctrl for RK3066

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-rk3066.c b/drivers/pinctrl/rockchip/pinctrl-rk3066.c
index 60e088a..f773f2a 100644
--- a/drivers/pinctrl/rockchip/pinctrl-rk3066.c
+++ b/drivers/pinctrl/rockchip/pinctrl-rk3066.c
@@ -82,7 +82,7 @@
 	PIN_BANK(6, 16, "gpio6"),
 };
 
-static struct rockchip_pin_ctrl rk3066_pin_ctrl = {
+static const struct rockchip_pin_ctrl rk3066_pin_ctrl = {
 	.pin_banks		= rk3066_pin_banks,
 	.nr_banks		= ARRAY_SIZE(rk3066_pin_banks),
 	.grf_mux_offset		= 0xa8,