[PATCH] USB Serial: clean tty fields on failed device open

If either the driver's open() method or try_module_get() fails, we need to
set 'tty->driver_data' and 'port->tty' to NULL in serial_open(), otherwise
we'll get an OOPS in usb_device_disconnect() when the device is disconnected.

Signed-off-by: Frank Gevaerts <frank.gevaerts@fks.be>
Acked-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>