Fix Busy State in temperature.cpp

Fix #11954

Marlin/src/module/temperature.cpp

         #define TEMP_CONDITIONS (wants_to_cool ? isCoolingHotend(target_extruder) : isHeatingHotend(target_extruder))
       #endif
 
-      #if DISABLED(BUSY_WHILE_HEATING)
-        #if ENABLED(HOST_KEEPALIVE_FEATURE)
-          const MarlinBusyState old_busy_state = gcode.busy_state;
-        #endif
+      #if DISABLED(BUSY_WHILE_HEATING) && ENABLED(HOST_KEEPALIVE_FEATURE)
+        const GcodeSuite::MarlinBusyState old_busy_state = gcode.busy_state;
         KEEPALIVE_STATE(NOT_BUSY);
       #endif
 
       wait_for_heatup = true;
       millis_t now, next_temp_ms = 0, next_cool_check_ms = 0;
 
-      #if DISABLED(BUSY_WHILE_HEATING)
-        #if ENABLED(HOST_KEEPALIVE_FEATURE)
-          const MarlinBusyState old_busy_state = gcode.busy_state;
-        #endif
+      #if DISABLED(BUSY_WHILE_HEATING) && ENABLED(HOST_KEEPALIVE_FEATURE)
+        const GcodeSuite::MarlinBusyState old_busy_state = gcode.busy_state;
         KEEPALIVE_STATE(NOT_BUSY);
       #endif