cpuidle / menu: move repeated correction factor check to init

In menu_select function we check for correction factor every time.
If it is zero we are initializing to unity. Hence move it to init function
and initialise by unity, hence avoid repeated comparisons.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Reviewed-by: Tuukka Tikkanen <tuukka.tikkanen@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>