kasan/test: fix protection against compiler elision

The kunit test is using assignments to
"static volatile void *kasan_ptr_result" to prevent elision of memory
loads, but that's not working:
In this variable definition, the "volatile" applies to the "void", not to
the pointer.
To make "volatile" apply to the pointer as intended, it must follow
after the "*".

This makes the kasan_memchr test pass again on my system.  The
kasan_strings test is still failing because all the definitions of
load_unaligned_zeropad() are lacking explicit instrumentation hooks and
ASAN does not instrument asm() memory operands.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 5f1c810 ("mm:kasan: fix sparse warnings: Should it be static?")
Signed-off-by: Jann Horn <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Dmitriy Vyukov <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Nihar Chaithanya <[email protected]>
Cc: Vincenzo Frascino <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: thejh

mm/kasan/kasan_test_c.c

@@ -47,7 +47,7 @@ static struct {
  * Some tests use these global variables to store return values from function
  * calls that could otherwise be eliminated by the compiler as dead code.
  */
-static volatile void *kasan_ptr_result;
+static void *volatile kasan_ptr_result;
 static volatile int kasan_int_result;
 
 /* Probe for console output: obtains test_status lines of interest. */