lkdtm: fix stack protector trigger

The -fstack-protector compiler flag will only build stack protections if
a character array is seen. Additionally, the offset to the saved
instruction pointer changes based on architecture, so stomp much harder
(64 bytes) when corrupting the stack.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>