Print active extruder with M105 for MAX6675

Was omitted when T0 is a MAX6675.

Marlin/Marlin_main.cpp

 
   #if HAS_TEMP_0 || HAS_TEMP_BED || defined(HEATER_0_USES_MAX6675)
     SERIAL_PROTOCOLPGM(MSG_OK);
-    #if HAS_TEMP_0
+    #if HAS_TEMP_0 || defined(HEATER_0_USES_MAX6675)
       SERIAL_PROTOCOLPGM(" T:");
       SERIAL_PROTOCOL_F(degHotend(target_extruder), 1);
       SERIAL_PROTOCOLPGM(" /");