USB: io_edgeport: fix use-after-free in TIOCMIWAIT

USB: io_edgeport: fix use-after-free in TIOCMIWAIT

commit 333576255d4cfc53efd056aad438568184b36af6 upstream.

Use the port wait queue and make sure to check the serial disconnected
flag before accessing private port data after waking up.

This is is needed as the private port data (including the wait queue
itself) can be gone when waking up after a disconnect.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>