[2.0.x] Fix compile error (#11951)

Fix compile error intruduced with M109 modification

Marlin/src/gcode/temperature/M104_M109.cpp

   #endif
 
   const bool no_wait_for_cooling = parser.seenval('S'),
-             set_temp = no_wait_for_cooling || parser.seenval('R')
+             set_temp = no_wait_for_cooling || parser.seenval('R');
   if (set_temp) {
     const int16_t temp = parser.value_celsius();
     thermalManager.setTargetHotend(temp, target_extruder);