drm/i915: Set the error code after failing to insert new offset into mm ht.

Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem.c

@@ -1288,6 +1288,7 @@ i915_gem_create_mmap_offset(struct drm_gem_object *obj)
 	list->hash.key = list->file_offset_node->start;
 	if (drm_ht_insert_item(&mm->offset_hash, &list->hash)) {
 		DRM_ERROR("failed to add to map hash\n");
+		ret = -ENOMEM;
 		goto out_free_mm;
 	}