Merge pull request #813 from drf5n/PID_DEBUG

temperature.cpp: Fix PID_DEBUG compile error.

Marlin/temperature.cpp

@@ -449,7 +449,8 @@ void manage_heater()
           pid_output = constrain(target_temperature[e], 0, PID_MAX);
     #endif //PID_OPENLOOP
     #ifdef PID_DEBUG
-    SERIAL_ECHO_START(" PIDDEBUG ");
+    SERIAL_ECHO_START;
+    SERIAL_ECHO(" PID_DEBUG ");
     SERIAL_ECHO(e);
     SERIAL_ECHO(": Input ");
     SERIAL_ECHO(pid_input);