apparmor: simplify sysctls with register_sysctl_init()

Using register_sysctl_paths() is really only needed if you have
subdirectories with entries. We can use the simple register_sysctl()
instead.

Acked-by: John Johansen <john.johansen@canonical.com>
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>