scan also 3rd available bus

src/drivers/px4flow/px4flow.cpp

@@ -674,10 +674,20 @@ start()
 			goto fail;
 		}
 
+		if (OK != g_dev->init()) {
+			delete g_dev;
+			/* try 3rd bus */
+			g_dev = new PX4FLOW(PX4_I2C_BUS_ONBOARD);
+
+			if (g_dev == nullptr) {
+				goto fail;
+			}
+
 			if (OK != g_dev->init()) {
 				goto fail;
 			}
 		}
+	}
 
 	/* set the poll rate to default, starts automatic data collection */
 	fd = open(PX4FLOW_DEVICE_PATH, O_RDONLY);