drm/ttm: Remove redundant code in ttm_tt_init_fields

Remove redundant assignment code for ttm->caching as it's overwritten
just a few lines later.

v2:
 - Update the commit message.
Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230531053051.3453509-1-Jun.Ma2@amd.com

drivers/gpu/drm/ttm/ttm_tt.c

@@ -137,7 +137,6 @@ static void ttm_tt_init_fields(struct ttm_tt *ttm,
 			       unsigned long extra_pages)
 {
 	ttm->num_pages = (PAGE_ALIGN(bo->base.size) >> PAGE_SHIFT) + extra_pages;
-	ttm->caching = ttm_cached;
 	ttm->page_flags = page_flags;
 	ttm->dma_address = NULL;
 	ttm->swap_storage = NULL;