patch 8.1.1182: some function prototypes are outdated

Problem:    Some function prototypes are outdated.
Solution:   Update function prototypes. (Ken Takata, closes #4267)
diff --git a/src/window.c b/src/window.c
index 4dda512..4ca5627 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4302,7 +4302,7 @@
  * Returns the specified window if the neighbor is not found.
  */
     win_T *
-win_horz_neighbor(tabpage_T *tp, win_T * wp, int left, long count)
+win_horz_neighbor(tabpage_T *tp, win_T *wp, int left, long count)
 {
     frame_T	*fr;
     frame_T	*nfr;