lib/test_stackinit: Fix static initializer test

lib/test_stackinit: Fix static initializer test

BugLink: https://bugs.launchpad.net/bugs/1946802
commit f9398f15605a50110bf570aaa361163a85113dd1 upstream.

The static initializer test got accidentally converted to a dynamic
initializer. Fix this and retain the giant padding hole without using
an aligned struct member.

Fixes: 50ceaa95ea09 ("lib: Introduce test_stackinit module")
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210723221933.3431999-2-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>