Fix EFM32 pwmout hal function pwmout_period

In pwmout_period() is a check for changed values, which is not working because of a wrongly used bitmask. This is fixed now.

Author: MikeDK

targets/TARGET_Silicon_Labs/TARGET_EFM32/pwmout_api.c

@@ -302,7 +302,7 @@ void pwmout_period(pwmout_t *obj, float seconds)
     }
 
     //Check if anything changed
-    if(((PWM_TIMER->CTRL & ~_TIMER_CTRL_PRESC_MASK) == (pwm_prescaler_div << _TIMER_CTRL_PRESC_SHIFT)) && (TIMER_TopGet(PWM_TIMER) == cycles)) return;
+    if(((PWM_TIMER->CTRL & _TIMER_CTRL_PRESC_MASK) == (pwm_prescaler_div << _TIMER_CTRL_PRESC_SHIFT)) && (TIMER_TopGet(PWM_TIMER) == cycles)) return;
 
     //Save previous period for recalculation of duty cycles
     uint32_t previous_period_cycles = PWM_TIMER->TOPB;