lkdtm: include WARN format string

In order to test the ordering of WARN format strings, actually include
one in LKDTM.

Link: http://lkml.kernel.org/r/1510100869-73751-2-git-send-email-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/lkdtm_bugs.c

@@ -63,9 +63,11 @@ void lkdtm_BUG(void)
 	BUG();
 }
 
+static int warn_counter;
+
 void lkdtm_WARNING(void)
 {
-	WARN_ON(1);
+	WARN(1, "Warning message trigger count: %d\n", warn_counter++);
 }
 
 void lkdtm_EXCEPTION(void)