haiku: Invert mouse wheel values to match what SDL expects.

Partially fixes Bugzilla #4442.

src/main/haiku/SDL_BApp.h

@@ -261,7 +261,7 @@ private:
             return;
         }
         win = GetSDLWindow(winID);
-        SDL_SendMouseWheel(win, 0, xTicks, yTicks, SDL_MOUSEWHEEL_NORMAL);
+        SDL_SendMouseWheel(win, 0, xTicks, -yTicks, SDL_MOUSEWHEEL_NORMAL);
     }
 
     void _HandleKey(BMessage *msg) {