opp: Reorder the code for !target_freq case

Reorder the code a bit to make it more readable. Add additional comment
as well.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Clément Péron <peron.clem@gmail.com>
Tested-by: Clément Péron <peron.clem@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>