mm/memory_failure: constify static mm_walk_ops

The only usage of hwp_walk_ops is to pass its address to
walk_page_range() which takes a pointer to const mm_walk_ops as
argument.

Make it const to allow the compiler to put it in read-only memory.

Link: https://lkml.kernel.org/r/20211014075042.17174-3-rikard.falkeborn@gmail.com
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -674,7 +674,7 @@ static int hwpoison_hugetlb_range(pte_t *ptep, unsigned long hmask,
 #define hwpoison_hugetlb_range	NULL
 #endif
 
-static struct mm_walk_ops hwp_walk_ops = {
+static const struct mm_walk_ops hwp_walk_ops = {
 	.pmd_entry = hwpoison_pte_range,
 	.hugetlb_entry = hwpoison_hugetlb_range,
 };