atomics: Constify loads: Fix powerpc build
Fixes: 5e9a82e898d5 ("atomics: Constify loads")
Sponsored by: The FreeBSD Foundation
(cherry picked from commit a9722e5ae8519a9a28e950dbd8d489178e9bc27e)
(cherry picked from commit 793939c9444dce957118fee412f5144c2e46aea3)