wlbuf_pool.h: add headers for forward declarations

This was previously implicitly included by the order of headers in
vo_dmabuf_wayland.c, but it is better to make it an explicit and reorder
the headers properly.

video/out/vo_dmabuf_wayland.c

@@ -40,9 +40,9 @@
 #endif
 #include "present_sync.h"
 #include "wayland_common.h"
+#include "wlbuf_pool.h"
 #include "generated/wayland/linux-dmabuf-unstable-v1.h"
 #include "generated/wayland/viewporter.h"
-#include "wlbuf_pool.h"
 
 struct priv {
     struct mp_log *log;

video/out/wlbuf_pool.h

@@ -15,6 +15,9 @@
  * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "wayland_common.h"
+#include "generated/wayland/linux-dmabuf-unstable-v1.h"
+
 struct wlbuf_pool_entry;
 
 typedef uintptr_t (*wlbuf_pool_key_provider)(struct mp_image *src);