ARM: EXYNOS: replace cpumask by the corresponding macro

A trivial patch to replace for_each_cpu(cpu_id, cpu_online_mask) by
the corresponding macro.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>