gps: reset RTCM instance

We need to reset the instance after looping through all instances.
Otherwise, we are left with the last instance if none is valid but have
not updated the _selected_rtcm_instance which is what is logged.

Therefore, this change fixes the logged RTCM instance.

Signed-off-by: Julian Oes <julian@oes.ch>

src/drivers/gps/gps.cpp

@@ -540,6 +540,9 @@ void GPS::handleInjectDataTopic()
 		}
 	}
 
+	// Reset instance in case we didn't actually want to switch
+	_orb_inject_data_sub.ChangeInstance(_selected_rtcm_instance);
+
 	bool updated = false;
 
 	// Limit maximum number of GPS injections to 8 since usually