kasan: clarify comment in __kasan_kfree_large

Currently it says that the memory gets poisoned by page_alloc code.
Clarify this by mentioning the specific callback that poisons the
memory.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://linux-review.googlesource.com/id/I1334dffb69b87d7986fab88a1a039cc3ea764725

mm/kasan/common.c

@@ -445,5 +445,5 @@ void __kasan_kfree_large(void *ptr, unsigned long ip)
 {
 	if (ptr != page_address(virt_to_head_page(ptr)))
 		kasan_report_invalid_free(ptr, ip);
-	/* The object will be poisoned by page_alloc. */
+	/* The object will be poisoned by kasan_free_pages(). */
 }