misc: lkdtm: bugs: At least try to use popuated variable

The result may not be intereresting, but not using a set variable
is bad form and causes W=1 kernel builds to complain.

Fixes the following W=1 warning(s):

drivers/misc/lkdtm/bugs.c: In function ‘lkdtm_STACK_GUARD_PAGE_LEADING’:
drivers/misc/lkdtm/bugs.c:331:25: warning: variable ‘byte’ set but not used [-Wunused-but-set-variable]
331 | volatile unsigned char byte;
| ^~~~
drivers/misc/lkdtm/bugs.c: In function ‘lkdtm_STACK_GUARD_PAGE_TRAILING’:
drivers/misc/lkdtm/bugs.c:345:25: warning: variable ‘byte’ set but not used [-Wunused-but-set-variable]
345 | volatile unsigned char byte;
| ^~~~

Cc: Kees Cook <[e-mail]>
Acked-by: Kees Cook <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/lkdtm/bugs.c

···
 
 	byte = *ptr;
 
-	pr_err("FAIL: accessed page before stack!\n");
+	pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte);
 }
 
 /* Test that VMAP_STACK is actually allocating with a trailing guard page */
···
 
 	byte = *ptr;
 
-	pr_err("FAIL: accessed page after stack!\n");
+	pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte);
 }
 
 void lkdtm_UNSET_SMEP(void)