USB: serial: ch341: fix open error handling

commit f2950b78547ffb8475297ada6b92bc2d774d5461 upstream.

Make sure to stop the interrupt URB before returning on errors during
open.

Fixes: 664d5df9 ("USB: usb-serial ch341: support for DTR/RTS/CTS")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>