backend/wayland: make destroy_wl_seats() handle a single seat

Instead of destroying all seats, destroy a single one. We only need
to destroy all seats at one call-site (backend_destroy), but we'll
need to destroy a single seat elsewhere in the next commit.

backend/wayland/backend.c

@@ -469,7 +469,11 @@ static void backend_destroy(struct wlr_backend *backend) {
 	wlr_drm_format_set_finish(&wl->shm_formats);
 	wlr_drm_format_set_finish(&wl->linux_dmabuf_v1_formats);
 
-	destroy_wl_seats(wl);
+	struct wlr_wl_seat *seat, *tmp_seat;
+	wl_list_for_each_safe(seat, tmp_seat, &wl->seats, link) {
+		destroy_wl_seat(seat);
+	}
+
 	if (wl->zxdg_decoration_manager_v1) {
 		zxdg_decoration_manager_v1_destroy(wl->zxdg_decoration_manager_v1);
 	}

backend/wayland/seat.c

@@ -246,9 +246,7 @@ bool create_wl_seat(struct wl_seat *wl_seat, struct wlr_wl_backend *wl) {
 	return true;
 }
 
-void destroy_wl_seats(struct wlr_wl_backend *wl) {
+void destroy_wl_seat(struct wlr_wl_seat *seat) {
-	struct wlr_wl_seat *seat, *tmp_seat;
-	wl_list_for_each_safe(seat, tmp_seat, &wl->seats, link) {
 	if (seat->wl_touch) {
 		wl_touch_release(seat->wl_touch);
 		wlr_touch_finish(&seat->wlr_touch);
@@ -274,7 +272,6 @@ void destroy_wl_seats(struct wlr_wl_backend *wl) {
 	wl_list_remove(&seat->link);
 	free(seat);
 }
-}
 
 bool wlr_input_device_is_wl(struct wlr_input_device *dev) {
 	switch (dev->type) {

include/backend/wayland.h

@@ -149,7 +149,7 @@ void init_seat_tablet(struct wlr_wl_seat *seat);
 void finish_seat_tablet(struct wlr_wl_seat *seat);
 
 bool create_wl_seat(struct wl_seat *wl_seat, struct wlr_wl_backend *wl);
-void destroy_wl_seats(struct wlr_wl_backend *wl);
+void destroy_wl_seat(struct wlr_wl_seat *seat);
 void destroy_wl_buffer(struct wlr_wl_buffer *buffer);
 
 extern const struct wlr_pointer_impl wl_pointer_impl;