drm/ttm: Fix memory leak in ttm_agp_backend.c

This patch fix a memory leak found by cppcheck.
[drivers/gpu/drm/ttm/ttm_agp_backend.c:129]:
(error) Memory leak: agp_be
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>

drivers/gpu/drm/ttm/ttm_agp_backend.c

@@ -126,6 +126,7 @@ struct ttm_tt *ttm_agp_tt_create(struct ttm_bo_device *bdev,
 	agp_be->ttm.func = &ttm_agp_func;
 
 	if (ttm_tt_init(&agp_be->ttm, bdev, size, page_flags, dummy_read_page)) {
+		kfree(agp_be);
 		return NULL;
 	}