cpufreq: davinci: call CPUFREQ_POSTCHANGE notfier in error cases

PRECHANGE and POSTCHANGE notifiers must be called in groups, i.e either both
should be called or both shouldn't be.

In case we have started PRECHANGE notifier and found an error, we must call
POSTCHANGE notifier with freqs.new = freqs.old to guarantee that sequence of
calling notifiers is complete.

Davinci driver was taking care of it but frequency isn't restored to freqs.old.

This patch fixes it.

Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>