mm/kfence: use str_write_read() helper in get_access_type()

mm/kfence: use str_write_read() helper in get_access_type()

Remove hard-coded strings by using the str_write_read() helper function.

Link: https://lkml.kernel.org/r/20250115155511.954535-2-thorsten.blum@linux.dev
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>