Added return in AsyncModbusSerialClient.connect (#1271)

Author: dries007

pymodbus/client/serial.py

@@ -121,6 +121,7 @@ async def connect(self):  # pylint: disable=invalid-overridden-method
         except Exception as exc:  # pylint: disable=broad-except
             txt = f"Failed to connect: {exc}"
             _logger.warning(txt)
+        return self.connected
 
     def protocol_made_connection(self, protocol):
         """Notify successful connection."""