lkdtm: clean up sparse warnings

Since lkdtm intentionally does "bad" things, we need to convince sparse
that we're doing these things on purpose. This adds an explicit cast
to the call to copy_to_user() and marks the spin lock as expecting
to dead-lock.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>