types/wlr_tablet_pad: constify impl

include/wlr/interfaces/wlr_tablet_pad.h

@@ -16,7 +16,7 @@ struct wlr_tablet_pad_impl {
 };
 
 void wlr_tablet_pad_init(struct wlr_tablet_pad *pad,
-	struct wlr_tablet_pad_impl *impl, const char *name);
+	const struct wlr_tablet_pad_impl *impl, const char *name);
 void wlr_tablet_pad_destroy(struct wlr_tablet_pad *pad);
 
 #endif

include/wlr/types/wlr_tablet_pad.h

@@ -24,7 +24,7 @@ struct wlr_tablet_pad_impl;
 struct wlr_tablet_pad {
 	struct wlr_input_device base;
 
-	struct wlr_tablet_pad_impl *impl;
+	const struct wlr_tablet_pad_impl *impl;
 
 	struct {
 		struct wl_signal button;

types/wlr_tablet_pad.c

@@ -6,7 +6,7 @@
 #include <wlr/types/wlr_tablet_pad.h>
 
 void wlr_tablet_pad_init(struct wlr_tablet_pad *pad,
-		struct wlr_tablet_pad_impl *impl, const char *name) {
+		const struct wlr_tablet_pad_impl *impl, const char *name) {
 	wlr_input_device_init(&pad->base, WLR_INPUT_DEVICE_TABLET_PAD, NULL, name);
 	pad->base.tablet_pad = pad;