um: Don't hardcode path as it is architecture dependent

commit 9ca19a3a upstream.

The current code fails to run on amd64 because of hardcoded reference to
i386

Signed-off-by: Ritesh Raj Sarraf <rrs@researchut.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>