Temp: have heater update on 250ms intervals.

Thermal managers (PID, bang-bang, etc.) assume they're being
ticked on 250ms intervals. In reality, they were being updated on
each temperature reading, which was between 10ms and 250ms. This
caused thermal management to malfunction.

https://github.com/Traumflug/Teacup_Firmware/issues/211

clock.c

@@ -84,6 +84,8 @@ static void clock_250ms(void) {
 		}
 	}
 
+  temp_heater_tick();
+
 	ifclock(clock_flag_1s) {
     #ifdef DISPLAY
       display_clock();

temp.c

@@ -393,10 +393,6 @@ void temp_sensor_tick() {
 				temp_sensors_runtime[i].temp_residency = 0;
 		}
 
-		if (temp_sensors[i].heater < NUM_HEATERS) {
-			heater_tick(temp_sensors[i].heater, temp_sensors[i].temp_type, temp_sensors_runtime[i].last_read_temp, temp_sensors_runtime[i].target_temp);
-		}
-
     if (DEBUG_PID && (debug_flags & DEBUG_PID))
       sersendf_P(PSTR("DU temp: {%d %d %d.%d}"), i,
                  temp_sensors_runtime[i].last_read_temp,
@@ -407,6 +403,21 @@ void temp_sensor_tick() {
     sersendf_P(PSTR("\n"));
 }
 
+/**
+  Called every 250ms from clock.c. Update heaters for all sensors.
+*/
+void temp_heater_tick() {
+  temp_sensor_t i;
+
+  for (i = 0; i < NUM_TEMP_SENSORS; i++) {
+    if (temp_sensors[i].heater < NUM_HEATERS) {
+      heater_tick(temp_sensors[i].heater, temp_sensors[i].temp_type,
+                  temp_sensors_runtime[i].last_read_temp,
+                  temp_sensors_runtime[i].target_temp);
+    }
+  }
+}
+
 /**
  * Report whether all temp sensors in use are reading their target
  * temperatures. Used for M116 and friends.

temp.h

@@ -36,6 +36,8 @@ void temp_init(void);
 
 void temp_sensor_tick(void);
 
+void temp_heater_tick(void);
+
 uint8_t	temp_achieved(void);
 
 void temp_set(temp_sensor_t index, uint16_t temperature);