lkdtm: silence warnings about function declarations

When building under W=1, the lack of lkdtm.h in lkdtm_usercopy.c and
lkdtm_rodata.c was discovered. This fixes the issue and consolidates
the common header and the pr_fmt macro for simplicity and regularity
across each test source file.

Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
index d70a417..fdf954c 100644
--- a/drivers/misc/lkdtm.h
+++ b/drivers/misc/lkdtm.h
@@ -1,6 +1,10 @@
 #ifndef __LKDTM_H
 #define __LKDTM_H
 
+#define pr_fmt(fmt) "lkdtm: " fmt
+
+#include <linux/kernel.h>
+
 /* lkdtm_bugs.c */
 void __init lkdtm_bugs_init(int *recur_param);
 void lkdtm_PANIC(void);
@@ -53,5 +57,4 @@
 void lkdtm_USERCOPY_STACK_BEYOND(void);
 void lkdtm_USERCOPY_KERNEL(void);
 
-
 #endif