MAINTAINERS: add myself as lkdtm maintainer

Officially claim maintainership over the LKDTM code.
Signed-off-by: Kees Cook <keescook@chromium.org>

MAINTAINERS

@@ -6580,6 +6580,11 @@ F:	samples/livepatch/
 L:	live-patching@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching.git
 
+LINUX KERNEL DUMP TEST MODULE (LKDTM)
+M:	Kees Cook <keescook@chromium.org>
+S:	Maintained
+F:	drivers/misc/lkdtm.c
+
 LLC (802.2)
 M:	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
 S:	Maintained