commit 88be12c4 upstream.

Otherwise we can get an oops if the user has no get_ref/put_ref
requirement.
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kurt Garloff <garloff@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>