drm/radeon: handle NULL bo->resource in move callback

The ttm bo now initially has NULL bo->resource, and leaves the driver
the handle that. However it looks like we forgot to handle that for
radeon.  It looks like this will just null-ptr-deref in
radeon_bo_move(), if bo->resource is NULL.

Fix this by calling move_null().

Fixes: 18025378 ("drm/ttm: stop allocating dummy resources during BO creation")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230208145319.397235-4-matthew.auld@intel.comReviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/radeon/radeon_ttm.c

@@ -213,7 +213,8 @@ static int radeon_bo_move(struct ttm_buffer_object *bo, bool evict,
 
 	rbo = container_of(bo, struct radeon_bo, tbo);
 	rdev = radeon_get_rdev(bo->bdev);
-	if (old_mem->mem_type == TTM_PL_SYSTEM && bo->ttm == NULL) {
+	if (!old_mem || (old_mem->mem_type == TTM_PL_SYSTEM &&
+			 bo->ttm == NULL)) {
 		ttm_bo_move_null(bo, new_mem);
 		goto out;
 	}