debugfs_create_*() returns NULL on error.  Make its callers return -ENODEV
on error.
Signed-off-by: NZhao Lei <zhaolei@cn.fujitsu.com>
Acked-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>