drm/ttm: fix unreachable code.

None of the in-tree drivers use user objects yet so this wasn't hitting
us.

Stanse found unreachable code in ttm_bo_add_ttm:
http://decibel.fi.muni.cz/~xslaby/stanse/error.cgi?db=32&id=714#l238Reported-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -275,9 +275,10 @@ static int ttm_bo_add_ttm(struct ttm_buffer_object *bo, bool zero_alloc)
 		bo->ttm = ttm_tt_create(bdev, bo->num_pages << PAGE_SHIFT,
 					page_flags | TTM_PAGE_FLAG_USER,
 					glob->dummy_read_page);
-		if (unlikely(bo->ttm == NULL))
+		if (unlikely(bo->ttm == NULL)) {
 			ret = -ENOMEM;
 			break;
+		}
 
 		ret = ttm_tt_set_user(bo->ttm, current,
 				      bo->buffer_start, bo->num_pages);