Fix a compile error: in sched_cpuload.c:Line136, the variables ts and secs are...

Fix a compile error: in sched_cpuload.c:Line136, the variables ts and secs are not defined if CONFIG_CPULOAD_ONESHOT_ENTROPY = 0. However, these variables are used regardless of CONFIG_CPULOAD_ONESHOT_ENTROPY at lines~180:onwards.