seccomp: simplify sysctls with register_sysctl_init()

register_sysctl_paths() is only needed if you have childs (directories)
with entries. Just use register_sysctl_init() as it also does the
kmemleak check for you.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>