USB: serial: ark3116: use port device for info and error messages

Use the port device rather than usb device in info and error messages.

This makes sure that driver and tty port is included in the messages,
while also making them more uniform.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>