backend: remove const casts for pixman_region32_t

Pixman 0.42.0 has constified APIs for pixman_region32_t. We no longer
need the casts.

backend/drm/atomic.c

@@ -240,11 +240,11 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 
 	uint32_t fb_damage_clips = 0;
 	if ((state->base->committed & WLR_OUTPUT_STATE_DAMAGE) &&
-			pixman_region32_not_empty((pixman_region32_t *)&state->base->damage) &&
+			pixman_region32_not_empty(&state->base->damage) &&
 			crtc->primary->props.fb_damage_clips != 0) {
 		int rects_len;
-		const pixman_box32_t *rects = pixman_region32_rectangles(
+		const pixman_box32_t *rects =
-			(pixman_region32_t *)&state->base->damage, &rects_len);
+			pixman_region32_rectangles(&state->base->damage, &rects_len);
 		if (drmModeCreatePropertyBlob(drm->fd, rects,
 				sizeof(*rects) * rects_len, &fb_damage_clips) != 0) {
 			wlr_log_errno(WLR_ERROR, "Failed to create FB_DAMAGE_CLIPS property blob");

backend/wayland/output.c

@@ -291,9 +291,9 @@ static bool output_commit(struct wlr_output *wlr_output,
 				output->surface);
 		}
 
-		pixman_region32_t *damage = NULL;
+		const pixman_region32_t *damage = NULL;
 		if (state->committed & WLR_OUTPUT_STATE_DAMAGE) {
-			damage = (pixman_region32_t *) &state->damage;
+			damage = &state->damage;
 		}
 
 		if (output->frame_callback != NULL) {
@@ -318,10 +318,10 @@ static bool output_commit(struct wlr_output *wlr_output,
 				0, 0, INT32_MAX, INT32_MAX);
 		} else {
 			int rects_len;
-			pixman_box32_t *rects =
+			const pixman_box32_t *rects =
 				pixman_region32_rectangles(damage, &rects_len);
 			for (int i = 0; i < rects_len; i++) {
-				pixman_box32_t *r = &rects[i];
+				const pixman_box32_t *r = &rects[i];
 				wl_surface_damage_buffer(output->surface, r->x1, r->y1,
 					r->x2 - r->x1, r->y2 - r->y1);
 			}

backend/x11/output.c

@@ -283,11 +283,10 @@ static bool output_commit_buffer(struct wlr_x11_output *output,
 
 	xcb_xfixes_region_t region = XCB_NONE;
 	if (state->committed & WLR_OUTPUT_STATE_DAMAGE) {
-		pixman_region32_union(&output->exposed, &output->exposed,
+		pixman_region32_union(&output->exposed, &output->exposed, &state->damage);
-			(pixman_region32_t *) &state->damage);
 
 		int rects_len = 0;
-		pixman_box32_t *rects = pixman_region32_rectangles(&output->exposed, &rects_len);
+		const pixman_box32_t *rects = pixman_region32_rectangles(&output->exposed, &rects_len);
 
 		xcb_rectangle_t *xcb_rects = calloc(rects_len, sizeof(xcb_rectangle_t));
 		if (!xcb_rects) {
@@ -295,7 +294,7 @@ static bool output_commit_buffer(struct wlr_x11_output *output,
 		}
 
 		for (int i = 0; i < rects_len; i++) {
-			pixman_box32_t *box = &rects[i];
+			const pixman_box32_t *box = &rects[i];
 			xcb_rects[i] = (struct xcb_rectangle_t){
 				.x = box->x1,
 				.y = box->y1,