Revert breaking change to _FAN_PWM macro

Marlin/src/module/temperature.cpp

       #endif
 
       #if ENABLED(FAN_SOFT_PWM)
-        #define _FAN_PWM(N) do{ \
-          const uint8_t spcf = (soft_pwm_count_fan[N] & pwm_mask) + (soft_pwm_amount_fan[N] >> 1); \
-          WRITE_FAN(N, (spcf > pwm_mask)); \
+        #define _FAN_PWM(N) do{                                     \
+          uint8_t &spcf = soft_pwm_count_fan[N];                    \
+          spcf = (spcf & pwm_mask) + (soft_pwm_amount_fan[N] >> 1); \
+          WRITE_FAN(N, spcf > pwm_mask ? HIGH : LOW);               \
         }while(0)
         #if HAS_FAN0
           _FAN_PWM(0);