[CPUFREQ] S3C64xx: Notify transition complete as soon as frequency changed

The CPUFREQ_POSTCHANGE notification is used to update things that depend on
the system clock rates. Since this may include the interfaces used to talk
to the regulators do the notification before we try to update regulators
to reflect lowered system clock rate.

The voltage scaling is just a power optimisation and may not happen at all
so there's no concern about it not having completed.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Dave Jones <davej@redhat.com>