The bc022f8cd8 introduces a static way to calculate idle stack address for risc-v platform. However, it uses the reverse order to access idle stack, which breaks boards with smp configuration. Correct the idle stack order of g_cpux_idlestack. Fixes: bc022f8cd8 ("arch/risc-v: unify idle stack calculation") Signed-off-by: Inochi Amaoto <inochiama@outlook.com>