The value of cxt->record_size does not change in the loop,
so this patch optimize the assign statement by dropping
sz entirely and using cxt->record_size in its place.

Signed-off-by: Wang Long <long.wanglong@huawei.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>