USB: serial: metro-usb: stop I/O after failed open

commit 2339536d upstream.

Make sure to kill the interrupt-in URB after a failed open request.
Apart from saving power (and avoiding stale input after a later
successful open), this also prevents a NULL-deref in the completion
handler if the port is manually unbound.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 70457786 ("USB: serial: metro-usb: get data from device in Uni-Directional mode.")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>