pinctrl: rockchip: constify rockchip_pin_ctrl for PX30

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-px30.c b/drivers/pinctrl/rockchip/pinctrl-px30.c
index cc7885b..4595d8a 100644
--- a/drivers/pinctrl/rockchip/pinctrl-px30.c
+++ b/drivers/pinctrl/rockchip/pinctrl-px30.c
@@ -324,7 +324,7 @@
 			    ),
 };
 
-static struct rockchip_pin_ctrl px30_pin_ctrl = {
+static const struct rockchip_pin_ctrl px30_pin_ctrl = {
 	.pin_banks		= px30_pin_banks,
 	.nr_banks		= ARRAY_SIZE(px30_pin_banks),
 	.grf_mux_offset		= 0x0,