cpuload: fix cpuload error

Signed-off-by: ligd <liguiding1@xiaomi.com>

sched/sched/sched_processtimer.c

@@ -225,11 +225,13 @@ void nxsched_process_timer(void)
       clock_timer();
     }
 
+#ifndef CONFIG_SCHED_CPULOAD_EXTCLK
   /* Perform CPU load measurements (before any timer-initiated context
    * switches can occur)
    */
 
   nxsched_process_cpuload();
+#endif
 
   /* Check if the currently executing task has exceeded its
    * timeslice.

sched/sched/sched_timerexpiration.c

@@ -382,11 +382,13 @@ static unsigned int nxsched_timer_process(unsigned int ticks,
   clock_update_wall_time();
 #endif
 
+#ifndef CONFIG_SCHED_CPULOAD_EXTCLK
   /* Perform CPU load measurements (before any timer-initiated context
    * switches can occur)
    */
 
   nxsched_process_cpuload_ticks(ticks);
+#endif
 
   /* Process watchdogs */