hostap: fix "registers" registration in procfs

The "registers" entry was incorrectly created in the procfs root instead
of the device specific directory.  Move "registers" registration
immediately after the containing procfs directory is created.

Signed-off-by: Mathieu Chouquet-Stringer <mchouque@free.fr>
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>