iris: Assert on mapping a tiled buffer without MAP_RAW

iris has never relied on detiled maps using hardware fences.
This code is a remnant of i965, where that was actually used.

We can just assert that callers don't do such a thing.

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10941>

src/gallium/drivers/iris/iris_bufmgr.c

@@ -1224,8 +1224,7 @@ void *
 iris_bo_map(struct pipe_debug_callback *dbg,
             struct iris_bo *bo, unsigned flags)
 {
-   if (bo->tiling_mode != I915_TILING_NONE && !(flags & MAP_RAW))
-      return iris_bo_map_gtt(dbg, bo, flags);
+   assert((flags & MAP_RAW) || bo->tiling_mode == I915_TILING_NONE);
 
    void *map;