Wayland: changed a few "SetError(); return -1;" to "return SetError()".

src/video/wayland/SDL_waylandmouse.c

@@ -356,8 +356,7 @@ Wayland_WarpMouseGlobal(int x, int y)
 static int
 Wayland_SetRelativeMouseMode(SDL_bool enabled)
 {
-    SDL_Unsupported();
-    return -1;
+    return SDL_Unsupported();
 }
 
 void

src/video/wayland/SDL_waylandvideo.c

@@ -324,8 +324,7 @@ Wayland_GetDisplayModes(_THIS, SDL_VideoDisplay *sdl_display)
 static int
 Wayland_SetDisplayMode(_THIS, SDL_VideoDisplay *display, SDL_DisplayMode *mode)
 {
-    SDL_SetError("SetDisplayMode not (yet?) supported on Wayland.");
-    return -1;
+    return SDL_Unsupported();
 }
 
 void

src/video/wayland/SDL_waylandwindow.c

@@ -186,8 +186,7 @@ int Wayland_CreateWindow(_THIS, SDL_Window *window)
     data->egl_surface = SDL_EGL_CreateSurface(_this, (NativeWindowType) data->egl_window);
     
     if (data->egl_surface == EGL_NO_SURFACE) {
-        SDL_SetError("failed to create a window surface");
-        return -1;
+        return SDL_SetError("failed to create a window surface");;
     }
 
     if (data->shell_surface) {