tower: Fix erroneous return value

The function's return value is void, not gboolean.

src/compositor/meta-texture-tower.c

@@ -410,7 +410,7 @@ texture_tower_revalidate_fbo (MetaTextureTower *tower,
   if (!cogl_framebuffer_allocate (fb, &catch_error))
     {
       cogl_error_free (catch_error);
-      return FALSE;
+      return;
     }
 
   cogl_framebuffer_orthographic (fb, 0, 0, dest_texture_width, dest_texture_height, -1., 1.);