Declare pid_output for PIDBEDTEMP

Marlin/temperature.cpp

   static float pid_error[EXTRUDERS];
   static float temp_iState_min[EXTRUDERS];
   static float temp_iState_max[EXTRUDERS];
-  // static float pid_input[EXTRUDERS];
-  // static float pid_output[EXTRUDERS];
   static bool pid_reset[EXTRUDERS];
 #endif //PIDTEMP
 #ifdef PIDTEMPBED
     #endif
 
     #ifdef PIDTEMPBED
-      pid_output = get_pid_output_bed();
+      float pid_output = get_pid_output_bed();
 
       soft_pwm_bed = current_temperature_bed > BED_MINTEMP && current_temperature_bed < BED_MAXTEMP ? (int)pid_output >> 1 : 0;