AP_GPS: Added const just to be explicit (NFC)

Signed-off-by: Dr.-Ing. Amilcar Do Carmo Lucas <amilcar.lucas@iav.de>

libraries/AP_GPS/AP_GPS.cpp

@@ -403,7 +403,7 @@ void AP_GPS::detect_instance(uint8_t instance)
 {
     AP_GPS_Backend *new_gps = nullptr;
     struct detect_state *dstate = &detect_state[instance];
-    uint32_t now = AP_HAL::millis();
+    const uint32_t now = AP_HAL::millis();
 
     state[instance].status = NO_GPS;
     state[instance].hdop = GPS_UNKNOWN_DOP;
@@ -612,7 +612,7 @@ void AP_GPS::update_instance(uint8_t instance)
 
     // we have an active driver for this instance
     bool result = drivers[instance]->read();
-    uint32_t tnow = AP_HAL::millis();
+    const uint32_t tnow = AP_HAL::millis();
 
     // if we did not get a message, and the idle timer of 2 seconds
     // has expired, re-initialise the GPS. This will cause GPS
@@ -786,7 +786,7 @@ void AP_GPS::setHIL(uint8_t instance, GPS_Status _status, uint64_t time_epoch_ms
     if (instance >= GPS_MAX_RECEIVERS) {
         return;
     }
-    uint32_t tnow = AP_HAL::millis();
+    const uint32_t tnow = AP_HAL::millis();
     GPS_State &istate = state[instance];
     istate.status = _status;
     istate.location = _location;
@@ -951,7 +951,7 @@ uint8_t AP_GPS::first_unconfigured_gps(void) const
 
 void AP_GPS::broadcast_first_configuration_failure_reason(void) const
 {
-    uint8_t unconfigured = first_unconfigured_gps();
+    const uint8_t unconfigured = first_unconfigured_gps();
     if (drivers[unconfigured] == nullptr) {
         gcs().send_text(MAV_SEVERITY_INFO, "GPS %d: was not found", unconfigured + 1);
     } else {