ARM: 8585/1: cpuidle: fix !cpuidle_ops[cpu].init case during init

Let's assume cpuidle_ops exists but it doesn't implement the according
init callback, current arm_cpuidle_init() will return success to its
caller, but in fact it should return -EOPNOTSUPP.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>