kexec: use ALIGN macro instead of open-coding it

Use ALIGN macro instead of open-coding it to improve code readability.

Link: https://lkml.kernel.org/r/20231212142706.25149-1-ytcoode@gmail.com


Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>