Fix return value of WhereIsFilament()

getFilamentPresent returns the state of the IO pin of the sensor.
So we should use AT_FSENSOR instead of IN_NOZZLE
since the fsensor does not know if the filament is actually in the nozzle.

Firmware/mmu2_fsensor.cpp

@@ -4,7 +4,7 @@
 namespace MMU2 {
 
 FilamentState WhereIsFilament(){
-    return fsensor.getFilamentPresent() ? FilamentState::IN_NOZZLE : FilamentState::NOT_PRESENT;
+    return fsensor.getFilamentPresent() ? FilamentState::AT_FSENSOR : FilamentState::NOT_PRESENT;
 }