USB serial: update the console driver

This patch (as1292) modifies the USB serial console driver, to make it
compatible with the recent changes to the USB serial core.  The most
important change is that serial->disc_mutex now has to be unlocked
following a successful call to usb_serial_get_by_index().

Other less notable changes include:

	Use the requested port number instead of port 0 always.

	Prevent the serial device from being autosuspended.

	Use the ASYNCB_INITIALIZED flag bit to indicate when the
	port hardware has been initialized.

In spite of these changes, there's no question that the USB serial
console code is still a big hack.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>