Merge pull request #1399 from beanz/use-bed-defines-not-extruder-ones

Code wont compile with extruder but without bed runaway protection defined.

Marlin/temperature.cpp

 
   #if TEMP_SENSOR_BED != 0
   
-    #ifdef THERMAL_RUNAWAY_PROTECTION_PERIOD && THERMAL_RUNAWAY_PROTECTION_PERIOD > 0
+    #if defined(THERMAL_RUNAWAY_PROTECTION_BED_PERIOD) && THERMAL_RUNAWAY_PROTECTION_BED_PERIOD > 0
       thermal_runaway_protection(&thermal_runaway_bed_state_machine, &thermal_runaway_bed_timer, current_temperature_bed, target_temperature_bed, 9, THERMAL_RUNAWAY_PROTECTION_BED_PERIOD, THERMAL_RUNAWAY_PROTECTION_BED_HYSTERESIS);
     #endif