AP_GPS: canonicalise statustext messages

Use "GPS %d" prefix, where %d is instance+1, to correspond
with parameters

libraries/AP_GPS/AP_GPS.cpp

@@ -964,13 +964,13 @@ void AP_GPS::_broadcast_gps_type(const char *type, uint8_t instance, int8_t baud
     if (baud_index >= 0) {
         hal.util->snprintf(buffer, sizeof(buffer),
                            "GPS %d: detected as %s at %d baud",
-                           instance,
+                           instance + 1,
                            type,
                            _baudrates[baud_index]);
     } else {
         hal.util->snprintf(buffer, sizeof(buffer),
                            "GPS %d: detected as %s",
-                           instance,
+                           instance + 1,
                            type);
     }
     GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, buffer);

libraries/AP_GPS/AP_GPS_UBLOX.cpp

@@ -812,7 +812,7 @@ AP_GPS_UBLOX::_parse_gps(void)
             _have_version = true;
             GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, 
                                              "u-blox %d HW: %s SW: %s",
-                                             state.instance,
+                                             state.instance + 1,
                                              _buffer.mon_ver.hwVersion,
                                              _buffer.mon_ver.swVersion);
             break;