cpuidle: ladder governor - use macro instead of hardcoded value

use CPUIDLE_DRIVER_STATE_START, instead of hardcoded value 0. As,
CPUIDLE_DRIVER_STATE_START can be 1/0 based on
CONFIG_ARCH_HAS_CPU_RELAX is defined or not.

Signed-off-by: Mohammad Merajul Islam Molla <meraj.enigma@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>